Full text of "Advanced biology"

See other formats

£Hf* f

Public From the collection of the

CONDITION

WHEN WHEN
SSUED RECEIVED

'P&

o Prejinger

v Jjibrary

f p

San Francisco, California
2006

M-

n» c^\~,

ADVANCED BIOLOGY

BY
FRANK M. WHEAT

Chairman, Department of Biology,
George Washington High School, New York
Instructor in Biology, New York University

AND

ELIZABETH T. FITZPATRICK

Chairman, Department of Health, Education,
George Washington High School, New York

im aiSt EYENIR6 hiU SCI1UUL

TTAN.

JLTJC

z miMMV

PRDPSKTY #F
tf> OF BUCiT^

NOV S 1929

In~W Y0*:K, ft. Y.

AMERICAN BOOK COMPANY

NEW YORK CINCINNATI CHICAGO

BOSTON ATLANTA

COPYBIQHT, 1929, BT

AMERICAN BOOK COMPANY
All rights reserved

AD. BIO. WH. AND FITZ.
W.P. 2

MADE IN U.8.A

DEDICATED TO TWO SUCCESSFUL PIONEERS

IN BIOLOGY TEXTBOOK MAKING

GEORGE W. HUNTER

AND

JAMES E. PEABODY

FROM WHOM THE AUTHORS OF THIS BOOK

RECEIVED THEIR EARLY TRAINING

AND INSPIRATION

PREFACE

Most adolescent boys and girls are more interested in themselves
than in abstract problems. Although colleges emphasize math-,
ematics and languages in their entrance requirements and say little
about science, there has been a rapid growth in the number of
sciences elected in the high schools. This is primarily due to the
realization that science is more a part of the lives of pupils than
other school subjects and an answer to more of their questions.
Youth is more interested in making direct observations and reason-
ing from them than in abstract thinking. There is a concerted
effort to ascertain the truth about phenomena and to find out how
and why things happen. Science teaches a valid method of inter-
preting evidence and helps one to arrive at logical conclusions.

In most secondary schools throughout the country elementary
biology or general science is taught in the first or second year.
There has been a growing demand for an advanced course in general
biology to follow the elementary science course. This text has been
written primarily to fill this need. The emphasis of the book is
on problems relating to human welfare. The origin and principles
of the development, structure, and functions of plants and lower
animals are introduced mainly as a background for the proper
understanding of human problems.

An interesting and novel feature of the text is the historical
treatment of many of the subjects, which gives the pupil a bird's-
eye view of the entire subject without overwhelming him with
unrelated facts. Teaching material is given at the end of each
chapter, designed to help the pupil in organizing, in his own mind,
the important principles discussed. The list of supplementary
readings offers the pupil sources of information other than the
text. All the laboratory problems necessary for a thorough

vi PREFACE

understanding and mastery of the subject are included. These
problems are usually given at the beginning of the chapters, so that
the pupil may find out for himself many of the facts given later in
the text. The pupil can exercise here the true scientific method :
examination, observation, and confirmation of his findings.

The plan of' presenting the subject matter is based on the prac-
tical experience in teaching this course for several years to high
school pupils by means of mimeographed lesson sheets prepared by
various members of the Biology Department of the George Washing-
ton High School, New York, N. Y. Changes in these sheets have
been made, but much of the material has been elaborated into the
present text. The enthusiasm of the Biology Department in the
George Washington High School is due largely to the inspiration and
support of Harold S. Campbell, Associate Superintendent of the
New York high schools. In his annual report of 1928 he included
the report of the District Superintendent of High Schools, Dr. John
L. Tildsley. In this report, Dr. Tildsley summarized the objectives
of science teaching and said :

"These objectives call for the creation of a more magnificent
self. They call for the expanding of the element of appreciation,
the kindling of imagination, the arousing of the sense of admiration
and wonder, the excitation of the emotions, the development of the
power of accurate observation, the desire for truth, courage to
follow the truth, and above all, the setting forth of science as 'a
'way of life.'"

The authors hope this text will open this broader "way of life"
and inspire pupils to think and to act magnificently.

Thanks are due the Biological Supply Co., New York, for the
use of photomicrographs prepared by Mr. Roy M. Allen, and also
to Miss Marjorie Fitzpatrick, Mr. Charles Inman, and Mr. Paul B.
Mann of New York city high schools, Prof. Ralph Cheney of Long
Island University, and Miss Ada Weckel of Oak Park, Illinois, high
school, for their critical reading of the manuscript.

CONTENTS

CHAPTER PAGE

I. The Biology of To-morrow 1

II. The Growth of Science 10

III. The Microscope ' 19

IV. The History of Cells 27

V. Functions of a Green Cell 34

VI. Typical Animal Cell . . . * 42

VII. The Resting and Dividing Cell 53

VIII. Structure of Higher Plants 66

IX. Human Tissues 73

X. Human Tissues (Continued) 83

XI. Food Nutrients 91

XII. The Teeth and Their Care 107

XIII. The Digestive System 114

XIV. Digestion and Absorption 125

XV. Blood and Its Importance 143

XVI. Circulatory System 151

XVII. Lymphatic System . . . . " . . . .163

XVIII. The Skin and Kidneys ....... 170

XIX. Respiration 177

XX. Metabolism 187

XXI. Ductless Glands 191

XXII. The Nervous System 202

XXIII. Nervous Reactions 215

XXIV. Mental Hygiene 227

XXV. How Life Began 239

XXVI. Asexual Reproduction 246

vii

Vlll CONTENTS

CHAPTER PAGE

XXVII. Vegetative Propagation . . . . . . 255

XXVIII. Sexual Reproduction 264

XXIX. Reproduction of Higher Plants 273

XXX. Reproduction of Animals 281

XXXI. Protection of Young 292

XXXII. Character of Offspring 306

XXXIII. Heredity 318

XXXIV. Mutations 335

XXXV. Plant and Animal Breeding 343

XXXVI. Eugenics 355

XXXVII. Progressive Development 371

XXXVIII. Bacteria . . . 391

XXXIX. Beneficial Activities of Bacteria .... 403

XL. Health 413

XLI. Smallpox and Its Control 420

XLII. Rabies and Its Control 429

XLIII. Tuberculosis and Its Prevention .... 437

XLIV. Diphtheria, Scarlet Fever, and Tetanus . . . 450

XLV. Typhoid Fever 464

XLVI. Certain Other Diseases 473

XLVII. The Control of Malaria and Yellow Fever . . 480

XLVIII. Defenses against Diseases 494

XLIX. Immunity 504

L. Taxonomy 510

Appendix 529

Index 551

CHAPTER I

THE BIOLOGY
OF TO-MORROW

Underwood and Underwood
Col. Charles Lindbergh.

Underwood and Underwood
Guglielmo Marconi.

At no time in the history of the world have the layman and the
scholar turned to the field of science for inspiration and help as in
the present age. We are all becoming more scientific-minded.
Man is leaving behind him the era of superstition and romanticism
and is seeking the truth in the light of science. Almost daily a
miracle happens — a discovery that thrills the world with its
tremendous import. Newspapers and periodicals devote column
after column to scientific matters, and even the writers of drama
and fiction go to science for plots. People discuss present-day
science as they once discussed literature.

The age of science. Do you recall how interested and excited
you were over the proposed New York to Paris flight of Charles
Lindbergh ? The entire nation followed the preparations and the
performance of the fearless and skillful lone pilot. All marveled
at the tiny monoplane with its speedy Wright whirlwind motor.
Nations rejoiced in the success of the experiment, and almost over-
night practically all people developed an interest in aviation. They
became air-minded. Since that time great progress has been made
in aviation, and travel by air over certain routes has become so
safe that few hesitate to sponsor this method of transportation.

Not only in aviation, but in radio, color photography, and

2 THE BIOLOGY OF TO-MORROW

television, experiments have been made and are followed with
intelligence and eagerness by great numbers of people. The radio

Ewing Galloway
Many of the problems of science are solved in the laboratory.

has brought the people of our nation together again and again.
In our own homes, by a turn of the dial, we take part in great
public gatherings miles away, enjoy a symphony, or listen to the
World Series baseball games. The transmission of the human voice
and of instrumental music through miles of space is now accom-
plished, with very little distortion. The reception of light waves,
bringing movies into every home, is a development of to-morrow.
There is as wide an interest in the subject matter of biology as
in other fields. The history of many scientific experiments and
investigations has been so wide spread that there is hardly a
school boy or girl who does not know the story of the control
of malaria and smallpox. The dramatic death of Hideyo Noguchi,
of the Rockefeller Institute, occurred at the culmination of years

WHAT OF YESTERDAY?

of work on yellow fever. Through his experiments, he revealed
to the entire world the painstaking methods characteristic of a
true scientist as well as the fearless persistence of a martyr.^

Noguchi had solved the problem of yellow fever in South America,
but the facts he found in that country did not seem to hold true for
the African type of the disease. He, therefore, journeyed to' Africa
to make further studies. He contracted the disease and died
before completing his work. He is one of the heroes of to-day.

What of yesterday? Consider the strides surgery has made
since the early days of this science. For generations the chief
medical and surgical treatments were sweating, bleeding, and
amputations. In the Lewis and Clark expedition in 1804, one of
the men became ill. Captain Clark described the treatment given
him. A big hole was dug in the ground and a fire was built
in it, in order to make the ground hot. Then the fire was re-
moved and the man was laid on the hot earth and securely
covered so that he would sweat. After this treatment he was
bled. Not having any other knife, Captain Clark used his pocket
penknife to open the blood vessel. Need-
less to say, the man died. Among primi-
tive people of to-day similar methods are
still in vogue. The medicine man in a
certain primitive tribe, still places people
in holes heated to high temperatures, to
sweat them. If a member of the tribe
suffers from chronic headaches, the medi-
cine man cuts a piece out of the sufferer's
skull.

In Civilized Communities, Surgery, aS Physicians of yesterday practiced

° v bleeding for many ailments.

a scientific study, began with the hypothe-
sis of Louis Pasteur, about 1860, that disease was usually due
to the presence of microorganisms. Realizing that most of
the surgical cases died from infections rather than the actual

THE BIOLOGY OF TO-MORROW

operation, Sir Joseph Lister (1827-1912) studied the work
of Pasteur. Up to this time pus was always considered the
necessary accompaniment of all wounds. Lister decided that
germs must enter the wound from the air, from surgical instru-
ments, or from other
outside agencies.
Thereafter, when oper-
ating, he used what he
called antiseptics to
kill the germs. He at-
tempted to destroy the
germs in the air by
spraying the air of the
operating room with a
carbolic acid solution.
He then protected the
wound as much as
possible from contact
with the air. All his instruments were subjected to the most
careful antiseptic treatments. He taught his principles of anti-
septic surgery to the surgeons of France. The Franco-German
War broke out in 1870. It occurred to no one in France, in the
first battles, to apply the new method of antiseptic surgery. In
consequence, hundreds and thousands of wounded soldiers suc-
cumbed to gangrene and septicaemia, types of blood poisoning.
Then doctors all over the world adopted antiseptic surgery. In-
fections which formerly followed many operations practically
disappeared. Before Lister's time 70 per cent of all compound
fractures resulted in death, and about 50 per cent of all major
operations were fatal. After Lister's antiseptic methods were in-
troduced these percentages were greatly reduced.

What of to-day ? The most modern method of surgery is aseptic
surgery. Germs are controlled by killing them with dry heat

An old print shows that headache was treated by removing
a portion of the skull.

WHAT OP TO-DAY?

rather than antiseptics. It is now known that the entrance of
germs into wounds is due to contaminated instruments or hands
rather than to air. If the hands of the doctor and the body of
the patient are washed with antiseptics and the instruments are
thoroughly sterilized, there is very little chance of contamination
from the air. The spraying of antiseptics in the air is no longer
done. To-day, less than one per cent of the patients subjected
to operation for compound fractures die.

Many of the mistakes of yesterday prevail even to-day. Along
with pure science come the pseudo-sciences. For example,
people were taught that definite areas, of the brain controlled
definite mental activities like motor control, vision, and judgment.
Immediately the pseudo-science, phrenology, came into being.
Phrenologists examined the various bumps on the head and
claimed that these were related to the development of areas *of
the brain. They argued that ^success in selling, teaching, or ex-
ecutive ability could be predicted
if the proper irregularities were
present on the person's skull. But,
through many years of observation
and experimentation, it has been
conclusively proved that the irreg-
ularities in the skull do not neces-
sarily follow brain irregularities.
With the invention of the radio and
television came a revival in the be-
lief in telepathy and spiritualism.

Interest in diets has led to fads
in foods. People were told raw
foods supplied vitamins. Some
people began to eat nothing but raw foods such as nuts, fruits, and
vegetables. Yeast was found beneficial in supplying a certain
vitamin, and was at once accepted, by some, as panacea for all ills.

Nurses who use antiseptic measures saye
as many lives as do doctors.

THE BIOLOGY OF TO-MORROW

Underwood and Underwood

What of to-morrow? The purpose of this book is to give a
scientific biological background to pupils so that they may have

a basis for discrimination be-
tween real and pseudo-science
in connection with the human
body. The aim of all science
is to ascertain the truth from
unbiased experiments with-
out regard to emotional preju-
dices or statements based on
speculation or imagination.
In scientific experimentation
one does not imagine or de-
cide beforehand what is going
to happen. Only actual ob-
servable facts are accepted.
If experiments on disease
were prejudiced, disease
would never be controlled.
Similarly, all life progresses
more efficiently when it is
lived scientifically. The sci-
entific, unemotional attitude

Forestry offers an opportunity for an out-of-door toward life's problems leads
life of service. to ft mQ ^ ex&ct so j ution>

It is hoped that the study of biology will be an inspiration to
recreational activities. Everyone is happy in the pursuit of a
hobby. It gives one a worthy use of leisure time. If this hobby
takes one out of doors, the result is usually beneficial to his health.
If certain facts about plants and animals are understood, an in-
telligent interest in their growth and habits is possible. News-
papers, magazines, books, and periodicals contain many scientific
articles and description of experiments. If a person has some

1 M

U. S. Forest Service

WHAT OF TO-MORROW? 7

knowledge of science, this wealth of material may be easily inter-
preted and understood by him. The present text aims to serve
as a basis for the interpretation of future scientific readings.
The more interests one can cultivate the more he gets out of life.
The relation of the biology of to-day to health cannot be over-
emphasized. One of the reasons why the people of yesterday
had so many fears concerning disease was that they were ignorant
of methods for preventing and controlling it. The prevention and
control of disease' can now be approached intelligently because
there has been some education along these lines. Cooperation be-
tween the public and the Board of Health is made possible because
of this health education. The general public understands what
the health authorities are trying to accomplish. Because it knows
that certain restrictions are formulated in the interests of health,
the public readily accepts and carries them out. For example,
there is not as much opposition to' the Schick test and the sub-
sequent immunization for diphtheria, as formerly, because the
public has been intelligently instructed concerning the need of
this scientific procedure to combat the disease.

■ ^^^^^^ M HP*' «h_

■ i

r U. S. Devi, of Agriculture

Wild blueberries. Cultivated blueberries.

Selection, cultivation and breeding have increased the size and flavor of many fruits.

When people cultivate proper personal habits and attitudes, and
more intelligent interests in the home and community, they achieve

THE BIOLOGY OF TO-MORROW

greater social and civic success. Biology helps to free people of
ignorant and useless racial customs. It is in school that proper
standards of cleanliness, ventilation, feeding, and routine are fre-
quently acquired. If hygienic habits of living are developed, and
people persist in practicing them, better social customs will soon be
established. For example, if students are taught the importance
of buying bread, wrapped to prevent contamination, and if they
insist on buying only wrapped bread, the storekeepers will soon
supply it. Weighing evidence in studying scientific data, develops
a control which makes the student approach family problems with
greater wisdom. Every individual owes certain responsibilities
to his community. Problems of sewerage, garbage disposal, street
cleaning, water and milk supply, control of disease are all discussed
in biology classes, and a better understanding of these will give
each person a clearer conception of his obligation to himself and
to the public.

The relation of biology to vocations. There are many voca-
tional opportunities in scientific fields. Biology suggests and
possibly lays the basis for many of these. The relation of biology
to the study of dentistry and medicine is obvious. The achieve-
ments of Pasteur, Koch, and Noguchi are fine ideals to arouse
enthusiasm and interest in research work. Bacteriology, chemical
analysis, and oral hygiene are laboratory fields that are intensely
interesting. Nursing is a vocation with a gripping human interest.

Science has improved the appearance, weight, and color of cattle.

TO-MORROW NEVER COMES

Underwood and Underwood Ewing Galloway

Agricultural progress has been made possible largely through scientific discoveries and

inventions.

Forestry, scientific farming, and animal and plant breeding are
vocations that constantly need more recruits. Biology has con-
tacts with all these vocations and is a means of giving students
such information that will help them to decide whether they
would like to pursue a scientific vocation.

To-morrow never comes. This book cannot give the latest
information about living things. Before it leaves the printer's
hands a new vitamin may be discovered, the cause and cure for
cancer may be announced, a new and unexpected theory may
necessitate a check and revision of much of the work that has
been set forth in these pages. If you who read are careful in
scrutinizing all data before you make a conclusion, you will have
become more scientific. You may be one who will add a chapter
to the biology of to-morrow ; you may learn and tell the farmers
of to-morrow how to grow two blades of grass where one formerly
grew. This Advanced Biology includes the story of the biology
of yesterday and of to-day. If it has been well told, it should
make your to-morrow a healthier, happier, and more complete day.

WH. FITZ. AD. BIO.

CHAPTER II

THE GROWTH
OF SCIENCE

Aristotle, Father of Biology.

Hippocrates, Father of Medicine.

What changes have taken place in science? What is science?
Into what branches may science be divided? What makes up bi-
ology ? How is biology related to other sciences ?

Science began when primitive man made an effort to explain
certain phenomena that he could not understand. Sickness
occasioned much speculation. Not knowing or understanding
anything about the various organs of the body, he thought disease
must be due to magic. Diseases were supposed to be caused by
evil spirits whose wrath had to be appeased or whose favor had to
be won. Ancient people burned sacrifices or beat tom-toms to
drive away the evil spirits. Some thought that diseases could be
transferred from man to animals. An example of this was the
belief that a toothache could be cured if the afflicted person stood
on the ground under an open sky, and spat in a frog's mouth,
asking the frog to take the toothache away. Another remedy sug-
gested, was to keep a hot, cooked, dried bean at the right elbow
for three days if the tooth ached in the left side of the mouth.
The order was reversed if the tooth was on the right side.

The advances of the Greeks. It was not until the time of Hip-
pocrates (born about 460 B.C.) that the Greeks began to attribute
disease to natural rather than to supernatural causes. Hippo-
crates taught that the body was in good health when the four juices,

EARLY SURGERY AND MEDICINE

blood, phlegm, yellow bile, and black bile, were mixed in the proper
proportions. Aristotle (384-322 B.C.) was one of the first men to
realize that all phenomena should be investigated very carefully
before a conclusion is made. He is called the Father of Bi-
ology because he made extensive studies of plants and animals
and their development. Not only did he investigate, but he
wrote down his investigations. He thus enabled the scientists
who followed, to build on his work. Because so little dissection
was permitted at this time, his work was full of errors ; but,
nevertheless, his studies were
of tremendous value. This
was the first step in breaking
away from idle speculation.
He started scientific investi-
gation, reason based on ob-
servation.

Early surgery and medi-
cine. Previous to the Middle
Ages, many scientists talked
and argued at great length
about health and disease, but
they were unable to make
scientific investigations be-
cause they were forbidden by
law to dissect the human
body. The only dissections
permitted were those of lower
animals such as dogs. Un-
skilled barbers usually made
these dissections for the scien-
tists. An instructor would

read to his class from an anatomy book written by a Greek phy-
sician, Galen. At the same time the barber pointed out the part

In the medical schools of the Middle Ages the
lecturer stood in a pulpit. Barbers made the
dissections and pointed out the structures as
they were mentioned. A few favored animals
received the discarded parts as they were cut off.

THE GROWTH OF SCIENCE

of the structure mentioned in the text. It was not until the time
of Vesalius (1514-1564) who lived in the Middle Ages, that surgery
was put on a professional basis rather than a menial one performed
by barbers and bath keepers. The study of the structure of the
human body was now both permitted and encouraged. No longer
was medical science purely speculative. It began to be based on
observation. In lecturing, Vesalius pushed aside the clumsy
surgeon barber and he himself demonstrated the parts of the dis-
sected body in a proper way. He began to draw pictures of the
dissections as he actually saw them. He disproved the old idea
that man differed from woman by having one less rib on one side.
He demonstrated by dissection that man and woman really have
the same number of ribs on each side. Gradually, teaching came
to be based on direct observation rather than opinion. As instruc-
tors acquired more and more knowledge of the human body, they
insisted on making their own dissections, instead of depending
upon the unscientific efforts of barbers. They realized the value
of careful dissections in order to show the structure of the body.

The efforts of physicians to look 'for
natural causes of disease rather than super-
natural was the beginning of science, but'
they did not go far enough. While scien-
tists were dissecting the human body and
disproving fallacies in regard to it, they
were not yet checking, experimentally, ob-
servations in the treatment of disease. For
example, when a patient's cure seemingly
followed the administration of some unusual
.remedy or drug, without further experi-
mentation, doctors jumped to the conclusion that they had dis-
covered the cure. During anepidemic of typhus fever, a Turkish
upholsterer, having become ill with the disease, drank some liquid
from a pail containing pickled cabbage, and recovered. Imme-

Before human dissections
were made, skeletons were
drawn very inaccurately.

THE MODERN SCIENTIFIC METHOD

Vesalius.'

One of his drawings.

Vesalius made many careful and accurate human dissections. He observed with exactness
and made records with rare skill.

diately, Turkish doctors declared cabbage juice was a cure for this
disease. The next patient died in spite of this treatment, so they
modified the prescription by saying that cabbage juice was a remedy
for typhus provided the patient be an upholsterer.

The modern scientific method. Compare these methods with
present-day methods in science. Imagination and speculation
have their place, but they are not to be confused with reasonable
judgment based upon experimentation and observation. A
scientist must have imagination and be able to predict what the
various causes of phenomena may be. Tfeen he must test out each
of his theories painstakingly under controlled conditions. This
testing method must be performed repeatedly in order to allow for
accidents. As a result of these experiments, observations are

14 THE GROWTH OF SCIENCE

made and conclusions drawn. This is the modern scientific method ;
science based on experimentation and observation.

Consider the work of Paul Ehrlich. He wanted to find a
chemical that had a deadly effect on certain microbes. First, he
studied these particular disease germs by staining them different
colors. Then he tried the effect of various chemicals on them.
With great patience he persevered, rejecting those tests that were
not satisfactory. Finally, his six hundred and sixth experiment
was successful. He had found a substance which would kill the
germ but would not injure healthy body tissue.

Dr. Thomas H. Morgan, University of California, is now work-
ing on the question of heredity. He has examined the size and
various body differences of tens of thousands of tiny flies. One
of the differences noted was a specimen with colorless instead of
pink eyes. He has bred this and other different types through
countless generations in his efforts to understand heredity. There
is no wild jumping to conclusions in his work. It is based on
definite, experimental evidence.

Think of the late Luther Burbank. Acres of ground were tilled,
planted, cultivated, and the plants were closely observed by this
experimenter. All but one or two plants grown were discarded in
his search for specimens of the plant he wanted to breed. He,
like other scientists, examined a wealth of data and then made a
careful selection from this material.

Contrast the cabbage juice treatment of typhus fever mentioned
before with the scientific investigation of malaria. It was first
observed that people living near swamps contracted a fever ; there-
fore, it was thought that swampy air caused this malady. The
disease was called malaria, meaning bad air. People were cau-
tioned to close their windows, particularly at night, to keep out the
bad air. Then, beginning with observations based on experimenta-
tion, doctors experimented with swampy air to see whether it would
give malaria or not. They found that it had no direct relation to

VIEWPOINTS OF SCIENCE 15

the disease. Then they hunted about for another probable cause.
Due to carefully controlled experiments, doctors were able to
demonstrate that malaria was caused by a definite microorganism
which was carried by a certain species of mosquito. Once this had
been demonstrated, the prevention, treatment, and cure of the
disease followed. Certain towns along the Canal Zone, for many
years infested with both malaria and yellow fever, have now become
health resorts. The carrier of the germ has been exterminated and
the disease is now under almost complete control.

Modern experimentation solves problems under controlled con-
ditions. The aim of the problem must be kept in mind, the method
of procedure must be decided upon, and all conditions carefully
regulated. All possible data must be painstakingly collected and
arranged in an orderly manner. Judgment must be suspended
until all the evidence has been properly weighed. All observa-
tions should lead to a logical conclusion which will give information
about the problem to be solved, if it does not actually solve it.
Such scientific observation leads to straight thinking. Science is
now becoming a philosophy of education rather than simply a
method, and is applicable to all problems of life.

Viewpoints of science. Human knowledge may be divided into
the arts and the sciences. Science is careful, exact, orderly
arranged knowledge. Among the many sciences are chemistry,
physics, and biology. Biology is that branch of science that deals
with living things or things that have been alive. The word
biology comes from two Greek words, bios — life ; logos — study.

In studying this earth on which we live, and the living things
that are found on our globe, the different scientists may each look at
the things about them from different points of view and use differ-
ent units upon which to build their sciences. In physics, the
scientist may separate a board into small chips or into sawdust,
and divide it further into smaller and smaller particles, finally,
reducing it to the smallest possible particle and still have the

THE GROWTH OF SCIENCE

material, wood. When the particles become so small that they
can be seen only with an ultramicroscope, they are called mole-
cules. The physicist calls everything that occupies space, matter;

and he thinks of matter as
being made up of tiny
molecules in motion.

The chemist takes sub-
stances or matter still fur-
ther apart. Water, wood,
rocks, air, our world in gen-
eral, may be taken apart
and separated into ninety-
two 'or more different sub-
stances called elements.
Ninety of these have been
separated from their com-
pounds and studied. Most
of the materials of the
world, including living things, exist in the form of compounds, com-
binations of elements. The chemist has worked out methods for
decomposing the compounds in order to study their constituents.
If an electric current is passed through water, it will cause the
liquid to be separated into two gases. If these two gases are col-
lected in tubes we find that twice as much gas will collect in one
tube as in the other. Both gases are colorless, odorless, and taste-
less. If a glowing splint is thrust into the tube containing the
smaller amount of gas, it will burn brightly — the gas supports com-
bustion. It is oxygen. If a lighted splint is held near the tube
holding the larger volume of gas, there is a slight explosion and
the gas burns with a blue flame. It is hydrogen. Water has been
separated into its elements, hydrogen and oxygen, and is shown
to consist of twice as much hydrogen as oxygen. The molecules
of these elements may further be divided into atoms. The chemist

Biology is related to chemistry and physics. The
topics embraced by both biology and chemistry have
been organized as a special science, bio-chemistry.
Note the other combinations shown in the diagram.

BIOLOGY A COMPLEX SCIENCE

^IIA^C

and physicist of to-day deal with matter in .even smaller particles,
as they have discovered that atoms are further divisible into
protons and electrons, that is, particles that carry positive^ and
negative electrical charges.

When a biologist looks at a living plant or animal he views it
in the light of his particular training. To some biologists, the
shape and form of the animal are of greatest interest. Others in-
vestigate the processes of the living organisms.

Biology a complex science. Many divisions of biology have
been investigated, and there is so much known about each one
that they are sometimes thought of as distinct subjects. The
specialist who delves in a particular division is named in terms of
the specialty he follows. The specialists who are interested in
the study of bacteria (bacteriology) are known as bacteriologists.
Protozoology, likewise, has
protozoologists who are in-
terested in one-celled ani-
mals. Those who study
snakes are interested in
herpetology ; the specialist
is a herpetologist. The en-
tomologist studies insects;
he is concerned with the
science of entomology.
Some scientists may special-
ize in only one branch
of entomology. Bugs are
classed as Hemiptera; stu-
dents interested in bugs are
hemipterists. Butterflies, the Lepidoptera, are the topic of study
of the lepidopterists. In each of these branches of biology we
have other subdivisions — morphology, the study of the forms and
structures, and physiology, the study of the functions of the organs.

Biology is a complex science made of many ologies.

18 THE GROWTH OF SCIENCE

Questions and Suggestions

1. Do you know of any superstitions that persist to-day in the
treatment of disease? Is there any scientific foundation for such
superstitions ?

2. What was the importance of the work of Vesalius ?

3. Who was Aristotle ?

4. Contrast the ancient method in treating disease with the modern
scientific way ?

5. In your research notebook define the divisions of biology repre-
sented in the diagram.

6. Give the proper names to the men who specialize in each division
noted.

7. a. List ten or more "ologies" not given in our outline.

b. Underline those "ologies" which might properly be included

in the circle of biology.

c. Place an m in front of the biological "ologies" just under-

lined, that are morphological, a p in front of the ones that
you think are physiological.

Supplementary Reading

Dana, Chas. L., Peaks of Medical History (Paul B. Hoeber [Medical Pub.]),

chaps, i-vi.
Locy, W. A., Biology and its Makers (Henry Holt & Co.).
Locy, W. A., Growth of Biology (Henry Holt & Co.).
Osborn, H. F., From the Greeks to Darwin (Charles Scribner's Sons).

CHAPTER III -=

THE
MICROSCOPE

An early microscope. How some were held.

How was the microscope invented? Was it much simpler at one
time or is it still in its original form ? What is the use of a microscope f
Is there a definite technique to be observed in using itf

Biology has contacts with other sciences. Inventions and dis-
coveries by physicists and chemists have made possible the explana-
tions of many biological facts. It is almost impossible to discuss
biology without including some physics and chemistry. The in-
vention and improvement of the microscope by physicists have
been largely responsible for the rapid progress of biology.

The history of the microscope. In Holland, in the seven-
teenth century, Anthony Von Leeuwenhoek (1632-1725) ex-
perimented "with lenses, grinding hundreds and using them in
various combinations to get different magnifications. He im-
proved those that had formerly been used. He used dust, wood,
and crystals to try the strength of his lenses. As he was interested
in natural history, he investigated the minute structure of living
things. He had little education and his researches were not con-
ducted on an extremely scientific basis, and, therefore, his work was
somewhat unsystematic and disconnected. However, his im-
proved lenses opened up an entirely new field, namely, the inves-
tigation of minute living things. Scientists could now actually
confirm certain of their speculations. A short time before the
microscope was improved, William Harvey, an English physician,

THE MICROSCOPE

had said that blood moved through the body in a circuit and that
the beating of the heart supplied the propelling force. He had
no microscope, but reasoned this out from observations made from
his dissections. Leeuwenhoek ground a lens to obtain proper
magnification, placed a tadpole in a glass tube, and adjusted the
tube in front of the fixed lens. When he looked through the lens,
he saw the blood, in the tail of the tadpole, come down one blood
vessel, cross to another, and return through still another. Thus,
by means of his lenses, he proved Harvey's reasoning was correct
in the specimen that he was studying. Leeuwenhoek did a great
deal to stimulate interest in perfecting the microscope. In his
day, for each new specimen studied a new lens had to be ground
and the object permanently fixed in relation to this magnifier.
To-day, microscopes are constructed quite differently. The lenses
are permanently mounted in relation to each other, forming

Concave
leflector*.

■lens

§4iC'i

all

Von Leeuwenhoek.

One of his many microscopes.
What he said:

What he saw.

"In the year 1675 I discover'd living creatures in Rain water which had stood but a few
days in a new earthen pot, glazed blew within. When these living Atoms did move they put
forth two little horns, continually moving themselves. They had a tayl, near four times the
length of the whole body, of the thickness (by my Microscope) of a Spider web; at the end
of which appeared a globul."

a compound microscope. We simply change the slides on which
the specimens are mounted. Many improvements have been made
in microscopes since the time of Von Leeuwenhoek, and the com-

THE HISTORY OF THE MICROSCOPE

One of Von Leeuwenhoek's microscopes con-
sisted of a lens, embedded in a large sheet of
copper with a movable rod which acted as a
mount for the specimen.

pound microscope of to-day is a very
complicated and delicate instrument.
It should always be handled with intel-
ligence and care.

Problem. Place a compound microscope
before you and find the various parts as they
are mentioned.

I. There are three distinct sets of parts :

A. The mechanical part supports the

other parts and makes possible their controlled movements.

B. The optical part does the actual magnifying which is made possible
by the rays of light passing through the lenses.

C. The illuminating part is used to direct and regulate the light.

II. All of the mechanical parts together constitute the stand, which has a
heavy base supporting a leg or pillar. Projecting horizontally from the top of
the pillar, parallel with the base, is the stage. There is a hole in the middle of
the stage through which the light passes. Above the stage is a continuation
of the pillar, and extending from this over the stage is the arm, which carries a
vertical tube. Projecting on both sides of the arm are disks with ridged edges.
These are connected with a pinion that causes the tube to go up or down when it

Von Leeuwenhoek placed a
small aquatic animal in a glass
tube which he fastened in
front of a microscope. Through
the lens he saw the circulation
of blood in the animal's tail.

THE MICROSCOPE

is turned. The larger disks with the rack and pinion make up the coarse adjust-
ment, or coarse adjustment screws. By turning the disks gently, you can see
the effect on the tube. The coarse adjustment is used to change the distance
between the lenses and the ^bject observed ; that is, to focus. Below the
coarse adjustment screws is a smaller pair of disks called the fine adjustment, or
fine adjustment screws. The fine adjustment is also used for focusing, but is

much more delicate than the
coarse adjustment.

III. The optical system
includes the part of the
microscope containing the
lenses. It consists of two
sets of lenses in metal cases.
The set placed at the lower
end of the tube, near the
object, is called the objective.
On most microscopes there is
a special attachment at the
base of the tube for carrying
two or more objectives con-
veniently; this is the nose-
piece. With the use of the
nosepiece it is possible to change from one objective to another with no loss of
time. The objective that is in line with the tube is the one in use. In general,
the longer the objective, the greater is the magnifying power. Most micro-
scopes have low-power and high-power objectives. At the top of the tube, near
the eye, is a set of lenses in a metal case called the eyepiece. This is easily
taken out of the tube.

IV. The illuminating system makes possible the adjustment and focusing
of the light on the object. It consists of the mirror, hung under the stage, and
of the diaphragm, inserted in the opening of the stage. The mirror usually has
two faces, one flat and one concave. The mirror can be turned in all directions
and is used for throwing a beam of light from the window (or suitable lamp)
upon the object and through the eyepiece, into the eye. The diaphragm
is an arrangement for enlarging or diminishing the amount of light coming
through the stage, by making the opening larger or smaller.

V. Some microscopes have a joint in the pillar just below the stage, permit-
ting the upper part of the stand to be tilted into a more convenient position.

The microscopes of to-day vary from the kind we use in our
school to those designed for elaborate research purposes.

DIRECTIONS FOR USING A MICROSCOPE

There are usually one or two clips fastened on the upper surface of the stage.
These are slipped over the edges of the slide to hold it stationary.

Professor R. H. Chambers has devised a microscope under which he can dissect out portions
of a cell or inject fluids into the different parts of the cell. The drawings (upper right) show
how he tears the cells apart. The other illustration is a photomicrograph showing a phase in
the actual operation.

Directions for caring for a microscope. In lifting or carrying
the microscope, grasp it firmly by the special handle above the
stage, and carry it in a horizontal position. Then the removable
parts cannot fall and break.

Allow nothing to touch any of the optical parts except espe-
cially prepared lens paper or a clean linen handkerchief, other-
wise the ground surfaces will be scratched.

Before putting the microscope away, turn the nosepiece so that
the objectives are not in a line with the tube. They are then
protected by the stage, and the microscope is not apt to be
damaged in placing it in the case.

Turn the clips in so they will not be broken.

Always follow the rules given below, for focusing.

24 THE MICROSCOPE

Rules fox* Focusing

1. Revolve the nosepiece until the shorter objective is in a direct
line with the tube. A click will be heard when this is'ttccomplished.

2. Place your prepared slide on the stage so that the specimen is in
the center of the opening of the stage.

3. Turn the mirror toward the nearest source of light. Manipulate
it until a bright area appears on the slide.

4. While looking at the microscope from one side, turn the coarse
screws clockwise until the low-power objective is one eighth of an inch
from the slide.

5. Then look through the eyepiece and turn the coarse adjustment
screws toward you (counterclockwise) until the specimen is clearly
seen. If you wish to see more of the specimen than is shown in the
field of vision, take hold of the slide with your thumbs and slowly
move it in different directions.

6. Turn On your high-power objective. Listen for a click.

7. Use your fine adjustment screws. Turn them carefully (clock-
wise) until xne object is clearly seen. The fine screws should be used
constantly in focusing with high power in order to see all that can be
seen.

Problem. How does an object appear when seen through the micro-
scope ?

Material : Compound microscope, slide, cover slip, piece of printed paper
with very small type.

Method : Place a drop of water on the slide. Place a small piece of
printed paper in the water and cover with a cover slip. The piece of paper
is now mounted.

Lay the prepared slide on the stage, with the object as near as possible to the
center of the hole in the stage. Follow your rules for focusing under low power,
then under high power.

I. Look through the microscope at the printed letter.

II. Describe the texture of the paper as revealed.

III. Draw the single letter, preferably the letter " i," exactly as it appears
under the low power. Note any apparent change in position.

IV. By means of a ruler measure your drawing ; then measure the letter
unmagnified. How many times does the low power appear to magnify ?

PROBLEMS

V. Turn on the high power. Again draw the letter, or as much as you
can see of it, as large as it appears. Measure your drawing with your ruler
and see how many times the high power appears to magnify the letter.

VI. Have your teacher tell you how much the microscope really enlarges
the object with low and high power. Caution. Always find your object with
the low-power objective, then turn on
the high power. If you lose your high-
power focus, go back to low power and
refocus.

Problem. How do onion cells ap-
pear when viewed through the micro-
scope f

Cut an onion into halves or quarters.
Peel off one of the scalelike leaves.
By means of a pair of forceps or knife
strip the thin tissue from the inside of
the scale. Mount a part of it on a
glass slide in a drop of water and cover
with a cover glass. Be sure to flatten
your specimen before covering it. View
the material under the microscope.
Then remove cover glass, and stain
the material by adding a small drop of
dilute iodine solution. Again cover. Ob-
serve with low power, then high power.

I. The little divisions that make up
the onion membrane are called cells.

A. The boundary of each cell is
the cell wall.

B. Describe the color and shape
of these cells.

The cells of the onion tissue often show
the heavy, woody walls and the large vacuoles
that are characteristic of most plant cells.

II. Observe the position of the granular and clear areas. The granular
areas make up the living part of the cell and are composed of a material called
cytoplasm. The clear areas are the vacuoles or fluid-filled spaces in the cytoplasm.

III. Find a small dense area somewhere in the cytoplasm. This is the nucleus.
A. Each nucleus has two disklike structures called nucleoli. Try to

identify a nucleolus in a nucleus.

WH. FITZ. AD. BIO. — 3

/ O f

26 THE MICROSCOPE

IV. Make the following drawings in your research notebook :

A. A careful diagram of a group of cells five times as large as they
appear under low power.

B. A group of cells twice as large as they appear under high
power. Label cell wall, cytoplasm, vacuole, nucleus, nucleolus. Under
the drawing, in small figures, state how many times enlarged your draw-
ing has been made ; for example, X 4 ; X 5 ; X 2.

Questions

1. What is the difference between a simple and a compound micro-
scope ?

2. Classify the parts of a microscope into three divisions.

3. Name two effects a microscope has on objects.

4. Explain how to focus with the low power ; with high power.

5. Why can we focus only thin material with our compound
microscopes ?

6. How do you mount a specimen, for study under the compound
microscope ?

Supplementary Reading

Locy, W. A., Biology and Its Makers (Henry Holt & Co.).

Locy, W. A., The Growth of Biology (Henry Holt & Co.).

Traeger, Alfred, The Microscope (E. Leitz Inc., 60 East 10th St., N. Y.).

Robert Hooke's microscope.

CHAPTER IV

THE HISTORY
OF CELLS

What he said:

What he saw and drew.

" I took a good clear piece of Cork, and with a Pen-knife sharpened as keen as a Razor, J
cut a piece of it off, and thereby left the surface of it exceedingly smooth, then examining it
very diligently with a Microscope, me thought I could perceive it to appear a little porous,
much like a Honey-comb."

How were living things first investigated? What were some of the
results of these studies? What scientists contributed to this work?

The pages of history reveal how and by whom the terms used in
describing the cell have been given to the science of biology. It
was comparatively easy for us to find the structure of an onion cell
under the compound microscope, but it has taken scientists three
centuries to perfect the microscope and find out as much about
cells as is known to-day.

The cell as first described. With very crude lenses, arranged
something like those in our compound microscope, Robert Hooke
(1635-1703), an Englishman, examined a thin section of cork. He
saw little boxlike structures which he called cells. He drew
diagrams and published the results of his investigations. He saw
only the cell wall after the living matter had disappeared, but the
term cell, first used by him, has been retained.

The nucleus. Robert Brown (1773-1858) was a Scotchman.
He studied medicine and became a surgeon's mate of a British
regiment in Ireland. During his early years, and while connected
with the army, he collected and studied plants and became known
as a naturalist. In studying orchids, he discovered a structure in

28 THE HISTORY OF CELLS

the cells which he called the nucleus ; and later he found a like
structure in the cells of many other plants. He wrote the following
account of his discovery: "In each cell of a great part of the
orchid family, a single circular area, generally somewhat more
opaque than the membrane of the cell, is observable. The
nucleus of the cell is equally manifest in many other fam-
ilies. ..."

Theodore Schwann (1810-1882) found, as a result of careful
work, that all the animals he investigated were made of cells.
At »the same time a friend of. his, Matthias Schleiden, discovered
that all of the plants he observed were made of cells. In the
cells they studied, they both noted the nucleus that Brown had
first discovered. They then made the supposition that all living
things are made of cells. This became known as the cell theory,
and this theory, having since been checked and rechecked by
many scientists, and more facts added, is now accepted as a fact.

Protoplasm was discovered by a French naturalist, Felix Dujar-
din, in 1835, and named by Purkinje in 1840. But the scientist
who made the name protoplasm best known was Hugo von Mohl
(1805-1872). He was born in Stuttgart, Germany. He was
graduated in medicine from Munich, became a professor of phys-
iology at Berne, and later a professor of botany at Tubingen. He
observed and analyzed the cell contents and described the move-
ment in the cell of certain small bodies which later were termed
chloroplasts. These were later shown to be the structures that
contain green coloring matter. He brought into general use the
term protoplasm and the fact that it is a living, streaming, grow-
ing, dividing substance.

Problem. How do the cells of Elodca appear when viewed through the
microscope f

Examine the appearance of a single leaf of the Elodea. Mount it in
water and heat by holding in the palm of the hand for a few minutes. The
heating will activate the protoplasm. Focus with low, then high power.

PROTOPLASM, AN ACTIVE SUBSTANCE 29

By slowly changing the focus you will be able to see that the Elodea leaf
is made of more than one layer of cells.

I. What striking difference do you observe between Elodea and onion
cells ?

II. Describe the new structures that you observe in Elodea cells. These
are called chloroplasts or green color bearers.

III. Observe two conspicuous differences between the chloroplasts and the
rest of the cytoplasm.

IV. Trace the movement of the chloroplasts. Do they move around in
the individual cells or do they pass from cell to cell? Suggest a reason for
your answ r er. The chloroplasts are carried by the movement of the stream-
ing protoplasm.

V. Remove the cover glass, add a drop of dilute iodine, re-cover, and
mount again.

VI. Describe the structures you now observe, that were also present in the
onion cell.

VII. Make a diagram, times five, of a few of the cells of the Elodea. By
means of arrows, trace the pathway of the moving chloroplasts. Label cell
wall, cytoplasm, nucleus, vacuole, chloroplast.

Protoplasm, an active substance. The movement of protoplasm,
observed by you in Elodea, was first observed by Von Mohl. He
recognized that the living, streaming, moving protoplasm was / the
cause of the motion that we observed in our Elodea cells.

Another name should be* added to the list of those who devoted
a large amount of their time to the study of the cell. Max
Schultze, a German anatomist, in 1863, clearly brought out the
fact that protoplasm (nucleoplasm and cytoplasm) is the unit of
all physiological activities. Before his time, people thought that
plant cells were made of one kind of living material and animal
cells of another kind. Much has been added to the work of
Schultze, but many of the facts discussed in the following para-
graph are largely a result of his efforts.

The key to every biological problem is sought in the cell ; for
every living organism is, or at some time has been, a cell. As

THE HISTORY OF CELLS

cellwcril

plasma
membrane

nucleus
chloroplast

Vactcafe^*

a result of the studies of
the scientists previously
named, the cell theory was
further developed. It was
now stated that all plants
and animals are made of
cells and cell products.
The cell is the structural
and physiological unit of
the organism. The living
organism can perform cer-
tain functions because its
cells are adapted to per-
form these functions.
Other scientists, using this
theory as their basis, have
been able to show the im-

Compare the cells of Elodea shown in the diagram with portance of the Cell in the
those you studied under the microscope. •, ■> n •

development or organisms
and something of its importance in heredity. Many scientists
are still investigating the structure and functions of cells and
others are studying the cell in its relation to the development of
the organism. This work, in spite of the fact that three centuries
have passed, is still in a developmental stage.

Cellular nature of plants. The cells of green plants are not all
alike in size and shape. A narcissus leaf is made of many layers
of cells which vary in shape.

Problem. Study of the epidermis of the narcissus leaf.

I. Peel off a small strip of the thin lower surface (epidermis) of a narcissus
leaf. Mount it for study, and focus it under the microscope.

A . Describe two different kinds of cells that are seen.

B. Note the small oval opening between paired cells. Suggest a use
for these openings ; for the cells that form them.

CELLULAR NATURE OF PLANTS

II. Draw a few of the cells, making sure to include in your diagram, at
least two differently shaped ones.

Higher plants are composed of many cells, but certain plants
are very simple in structure. A green coating is frequently found
on the north side of many buildings and of most trees. This is
caused by the presence of thousands of tiny one-celled, green
plants called Pleurococcus.

Problem. Study of Pleurococcus.

I. Scrape some of the green material on to a slide, mount in water, and
study with low and high magnification. Describe the shape, color, and struc-
ture of the cells.

II. Draw a single cell and a group of cells. Label cell wall, the very large
chloroplast which almost fills the cell, and the nucleus.

III. Write a description of what you have seen and tell how Pleurococcus
differs from Elodea and narcissus cells.

A typical green cell that is easy to study is Spirogyra. As it
floats on the surface of ponds, it looks like a tangled mat of
green threads or hairs. A
common name for it is pond
scum or frog's "spittle."
This latter name is given to
it because it is slimy in tex-
ture and is found in the same
habitat with frogs. Many
people at one time thought
that the frogs spit it out.

Problem. Study of the cells
of Spirogyra.

By means of forceps and a pair
of scissors detach a few strands of

Spirogyra. Mount them on a slide and cover with a cover slip,
the specimen under the low power.

A photomicrograph of the lower surface of a leaf.

Focus

THE HISTORY OF CELLS

I. Describe the cellular structure of a single strand of Spirogyra. When-
ever unicellular plants exist singly, end to end, the formation is called a filament.

In reality, each cell is a complete unit and
in no way dependent on the adjoining cells.

II. Describe a structure in the cell that
suggests the reason for the name Spirogyra.
The name Spirogyra means coiling circles
(spira — coil; gyros — circle). What re-
semblance is there between a chloroplast of
Spirogyra and a chloroplast observed in the
Elodea ?

III. State the number of complete chlo-
roplasts observed in each cell of your
specimen.

A. State the number of complete
turns found in each chloroplast.

B. Using the words waVy, irregular,
or straight, describe the edge of the
chloroplast.

IV. Identify the cell wall and the fila-
ment sheaths. This sheath is gelatinous
and gives the strands their characteristic
slimy texture.

V. Draw a 'cell five times larger, than
the one observed under the low power.
Show in your drawing how the adjoining
cells lie in relation to the one drawn. Label
cell wall, filament sheath, chloroplast.

VI. Stain a cell with dilute iodine and focus under low power and then
under high power. Locate and describe the nucleus, nucleolus, and strands
of cytoplasm.

VII. Describe the location and suggest the nature of the contents of the
vacuoles left among the strands of cytoplasm. The part of the cytoplasm
inclosing the vacuoles is called the plasma membrane.

VIII. Locate the structures stained blue. These are specialized cyto-
plasmic structures called pyrenoids. What evidence is present that the pyre-
noids store starch?

-cytoplasm,
--vcccccole/
chloroplast

- nucleus*

-jy^renoia

..vccCLcqle. ^
containing

cell sap &
-celKvotfl

— filaments
sfteottVL

S'pirogyra is a single-celled plant.
These plants grow end to end and
thus form strands called filaments.

QUESTIONS 33

IX. Draw a complete cell of Spirogyra as observed under the high-power
objective. Label filament sheath, cell wall, strands of cytoplasm, plasma
membrane, vacuole, nucleus, nucleolus, spiral chloroplast, and pyrenoid.

X. Write a description of Spirogyra, mentioning all the parts that you saw.

The simplest plants have no root, stem,
nor leaves. Such plants are called Thal-
lophyta {thallus — shoot ; phyton — plant) .
The green thallophytes are called algae.
Their color is due to the presence of chloro-
plasts that vary in size and shape. The
algae that we have already studied are
Pleurococcus and Spirogyra. Other thai- ^ wm ^^^^ a ^ 9
lophytes lack chloroplasts and are usually

colorless. They are called fungi. Yeasts and molds are common
examples of fungi.

Questions

1. Outline in tabular form, the names of the scientists, their nation-
alities, century in which they worked, and their contributions to the
cell theory.

2. Draw as many labeled cells as are necessary to show cell wall,
nucleus, cytoplasm, vacuole, pyrenoid, and chloroplast.

3. Compare Spirogyra with another alga that you have studied.

4. What makes Spirogyra slimy ?

5. What is a reason for the name thallophytes ?

Supplementary Reading

Gager, C. S., General Botany (P. Blakiston's Son & Co.), chap. ii.

Haupt, A. W., Fundamentals of Biology, (McGraw-Hill Book Co. Inc.),

chap. iv.
Holman, L. A., and Robins, W. W., Textbook of General Botany (John Wiley &

Sons).
Holmes, S. J., General Biology (Harcourt, Brace & Co.), chap. iii.

CHAPTER V

FUNCTIONS OF
A GREEN CELL

Nature's food factory.

Some of the products.

What does a green cell use for foodf Where does it get this food?
What are the physiological activities of cells containing chlorophyll f

In order to live, a green cell must carry on certain functions. Be-
cause these functions are carried on within the organism they are
called physiological functions. These functions may be classified
as nutritive^ adaptive, and reproductive. The nutritive processes
can be further subdivided into absorption, food manufacture, food
storage, digestion, assimilation, secretion, growth, respiration, and
excretion. These have to do with the obtaining and the using or*
food. The adaptive processes have to do with the way the organism
maintains itself and behaves in its environment. The reproduc-
tive processes have to do with the producing of new individuals.

Absorption. The Spirogyra takes in carbon dioxide, water, and
mineral matter for the manufacture of food. These raw materials
are in the form of gases and solutions and enter through the cell
membrane. They remain in the vacuoles until they are needed.
Oxygen, also, is taken in during the breathing process. The
process by which material passes through a cell membrane is called
osmosis or absorption. Many theories are advanced to explain
this activity ■; but probably no-one theory holds under all condi-
tions. According to one explanation there are minute openings in
the membrane through which the liquid or gas passes.

ABSORPTION 35

According to the molecular theory, all matter, whether solid,
liquid, or gas, consists of molecules in constant motion. The mole-
cules of solids are close together and there is very little space for
them to move. There is more space between the molecules of
liquids, and still more between those of gases. Consequently,
molecules of liquids move more freely than those of solids, and
molecules of gases move even more freely than those of liquids.

As the molecules in gases or solutions keep bounding up
and down, knocking against each other and against the cell mem-
brane, some of them move through the small openings. If the
molecules are very active, as in gases or certain liquids, these
molecules can pass readily through the membrane. The mole-
cules of denser liquids move more slowly and therefore will take a
longer time to go through the membrane. In general, the rate of
osmosis of a substance depends upon the number of its molecules.
During the process of osmosis the molecules of any substance
pass through a permeable membrane more rapidly from the area
of greater concentration to an area of lesser concentration. Osmosis
never stops, although when there is a balance of materials on
either side of the membrane, there may be so even an exchange
of molecules that osmosis is not obvious. When the membrane
is a living one, as in the cell membrane, the cytoplasm exercises
a definite selective action, taking in and keeping in the materials
needed by the cell and eliminating those not needed.

Demonstration. To illustrate the movement of molecules.

Make a very dilute solution of powdered carmine or India ink in water.
Place a drop under the compound microscope and observe under both low and
high magnification.

Describe the behavior of the particles observed in this experiment.
According to the molecular theory, molecules are always in a state of motion
somewhat similar to that of the particles observed by you.

Robert Brown, who was the first person to observe the nucleus
in plant cells, first described the movement that you have just

36 FUNCTIONS OF A GREEN CELL

observed. This is called the Brownian motion. Modern physics
teaches that molecules move not only in solution and during
osmosis, but that the molecules of all matter are constantly bom-
barding each other. The desk on which you write is composed
of tiny particles not inseparably cohering and sticking to each
other, but in a slight, constant state of activity similar to that
which you observed in the particles under the microscope.

Food manufacture. A green cell is one containing certain organ-
ized and specialized cytoplasm, called chloroplasts. There is
found in these chloroplasts a complex, green material, chlorophyll,
which is necessary for the manufacture of food. The green cell is
independent because it does not rely on other organisms for its
food ; it manufactures its own. All cells, whether green or not, need
carbohydrates (sugar and starches), fat, and protein. The cells
manufacturing foods always absorb two compounds : a gas, carbon
dioxide (C0 2 ), and water (H 2 0). These raw materials get through

O -for Ojci&<jdforL-

co 2

■ «£ energy

'^nitrates. *
sctlpHcL-tes,
pHospHate^

There is a continuous income and outgo of gases during respiration and photosynthesis.

the cell wall and plasma membrane by the process of osmosis.
Then the chloroplasts by a number of complicated processes, with
the aid of sunlight, chemically tear apart the elements of these
compounds, water and carbon dioxide, and recombine them into
simple carbohydrates. Since more oxygen is contained in the raw
materials than in the sugar manufactured, oxygen is given off
during the process. It is supposed by some that the elements

FOOD MANUFACTURE

carbon and oxygen, found in the compound carbon dioxide, chemi-
cally join with the elements hydrogen and oxygen, found in the
compound water, and give rise to a more complex compound of
carbon, hydrogen, and oxygen, probably formaldehyde. In this
chemical process, oxygen is left over and is given off by the plant.

C0 2 + H 2

Carbon dioxide + Water

■>- CH 2 + 2

->- Formaldehyde + Oxygen

This process is one of the early
light ; syn ^— together ; tithemi -
Photosynthesis is the combining
chlorophyll, in the presence of
light, to make sugar.

The molecule of formalde-
hyde is then chemically joined
with other molecules of formal-
dehyde to make a simple sugar.
Further combining will build up
more and more complex sugars
such as monosaccharides, di-
saccharides, polysaccharides
(starch is in this group) . Some-
times other complex compounds
such as oils and fats are pro-
duced. These are often found
in cells as storage products.
They are again converted into
simpler forms of sugar when
they are to be used as fuel.

Sugar is also the basis for
the formation of proteins. In
order to manufacture protein —
a process known as protein-

steps in photosynthesis (phoso —
-place: light places together),
of carbon dioxide and water by

chromoplccsb

needle like

cHcstet*of

Cells may contain inclusions such as plastids
(color-bearing particles), starch granules or
crystals of various forms.

38 FUNCTIONS OF A GREEN CELL

synthesis — the plant absorbs minerals, in the form of nitrates,
sulphates, and phosphates, which are dissolved in soil water. These
substances furnish the plants with nitrogen, sulphur, and phos-
phorus which are thought to combine with some of the sugar to
form protein, a substance containing carbon, hydrogen, oxygen,
nitrogen, sulphur, phosphorus, and perhaps other minerals.
Protein in protoplasm may be represented by the symbols
C-H-O-N-S-P. Most protein is used for growth (protoplasm
making), repair, and storage. Some is decomposed and the sugar
(one of the products of decomposition) is burned as fuel, while
the other products are thrown out as nitrogenous wastes or stored
for further protein-synthesis.

Digestion. When the food substances that have been stored
in the cells of the plant as fats, starches, and proteins are to be used,
they must first be changed to a soluble form. The process of
changing an insoluble nutrient into a soluble form that can be
used by the organism is called digestion. Digestion is brought
about by the presence and action of chemical substances called
digestive enzymes. These act as catalytic agents, that is, they
bring about a chemical change, but are themselves not affected
by nor changed during the process. In the cell where digestion
takes place, there is an amylase for the breaking down of starch,
a protease for the digestion of proteins, a lipase for the digestion
of fats. (The names of most of the enzymes end in ase.) After
being digested, the liquid nutrients may be carried by means of
the streaming, flowing motion of the protoplasm to that part of
the cell where they are to be utilized. If there is an excess of
food nutrients, they may again be combined into an insoluble
form and stored in the cells until needed.

Respiration. Each living plant cell takes in oxygen through the
cell membrane and gives off carbon dioxide by means of diffusion.
The oxygen unites with the compounds of hydrogen, oxygen, and
carbon and releases the energy, in the form of heat, stored in them.

ASSIMILATION 39

This union is a type of oxidation. The energy released from
food was stored up at the time of the manufacture of food (photo-
synthesis and protein-formation) in a potential, latent or dormant
form. The sun is the source of this energy. When oxidation of
food occurs, the potential energy is converted and released as
kinetic, an active form of energy. In plant cells, the kinetic
energy takes the form of work energy or heat energy, resulting
in the maintenance of a normal temperature. As a part of this
oxidation process, wastes, carbon dioxide and water, are formed.

carbohydrate "bg^tjy cc ^rot^ii^

[CHpc(p( ICHadj^SP"

2 O*

\ releccsecl Y

er ^" ~ ~ u r\~Z nitrogenous

The green plant cell builds up carbohy- A protein may be broken down during oxi-

drates which contain bound-up energy. This dation and energy released. Among the
may later be set free as heat or work energy. resulting wastes are some containing nitrogen.

These the cell gives off. If respiration takes place at the time
the plant is actively making sugar, the carbon dioxide and some
of the water resulting from oxidation may be retained for further
photosynthesis. Nitrogenous wastes are probably retained for
further manufacture of protein. The oxygen released during
photosynthesis may be retained for oxidation although it is usually
given off. Thus a balance of materials may be maintained. Res-
piration, then, involves the taking in of oxygen, the oxidizing of
. certain food materials present, and releasing energy and waste
products. The respiration process is the means of releasing all of
the energy needed by the plant.

Assimilation. The protoplasm of the cell is built of the elements
C-H-O-S-N-P, and sometimes others. After protein manufac-
ture is accomplished, the lifeless protein together with water and

FUNCTIONS OF A GREEN CELL

mineral materials may ultimately be transformed into living plant
protoplasm. Scientists have not determined just how this trans-

n i -*

, "more

cell
Bivision.

A green cell makes and assimilates food. Growth occurs. When no further growth is pos-
sible, the nucleus elongates, divides, and then the cell divides. Thus two cells are formed.

formation takes place. The name given to the change of a soluble
protein into living protoplasm is called assimilation. True growth
in an individual cell is due to the increase in the sum total of the
amount of protoplasm resulting from assimilation. Cells may also
increase in size, temporarily, when the cell vacuoles become filled
with an abundance of watery sap. The entire plant organism
grows by enlargement of the individual cells, until they attain a
certain size. Then they divide, causing an increase in the total
number of cells. This process of cell division will be discussed later.

Excretion. Any product given off through the cell wall as waste
is called an excretion. If a product is built up and given off for a
further use in the organism, it is called a secretion. Often, some
oxygen formed during food manufacture is held and used for oxi-
dation. The waste products from oxidation of sugars are carbon
dioxide and water. When these wastes are not retained by the
cell for further food making, they are excreted through the cell wall.

Irritability. There are many substances and forces, called
stimuli, that act upon a green plant cell. A cell is spoken of as
being sensitive or irritable to light, temperature, touch, chemicals,
electricity, and many other stimuli. The real cause of the effects
produced by these stimuli is to be found in the nature of pro-
toplasm. It is the protoplasm" that is irritable. Response is the
name given to the reaction the organism makes to the stimulus.
We have seen the effect on the protoplasm of the Elodea cell by

CELL DIVISION 41

holding it in a warm hand for a few seconds. Other stimuli have
other effects depending upon the sensitiveness of the particular cell.
Cell division. A plant cell has a certain limit of size beyond
which it does not grow. When this limit is reached, the nucleus
may elongate and divide, producing two nuclei. There is a wall
formed across the cell dividing the protoplasm into two parts,
each containing one of the daughter nuclei.

Questions

1. Why may chlorophyll be considered the source of the food supply
of the world ?

2. Discuss the transformations of energy in a green plant.

3. If green plants are eaten by animals, what additional trans-
formations of energy may result ? '

4. Compare the oxidation of food in the plant cell with the oxidation
of coal in the school furnace, giving points of similarity and difference.

5. Compare respiration in a green plant cell with photosynthesis,
considering materials used, products formed, products excreted, and
the purpose of the functions.

6. Why may carbon be considered the real fuel of a green cell ? In
what form did it enter the cell? In what form did it ultimately
leave the cell ? Name all physiological functions involved in the use
of carbon.

7. Trace the probable source of the carbon in coal.

8. Discuss a balanced aquarium, stating the give and take of
materials between fish and green plants.

9. In the figure on page 36 the possible intake and outgo of
materials in a green cell are shown. What are the actual interchanges
of materials ?

Supplementary Reading

Coulter, Barnes, and Cowles, A Textbook of Botany (American Book Co.),

Vol. I.
Gager, C. S., General Botany (P. Blakiston's Son & Co.).
Holmes, S. J., General Biology (Harcourt, Brace & Co.), chap. vii.

WH. FITZ. AD. BIO.

CHAPTER VI

TYPICAL
ANIMAL CELL

and of Paramecium.

Photomicrographs of Amoeba

Bo animals ever consist of single cells f Can the simplest of animals
be easily recognized as animals f Bo they appear different from one-
celled plants? Bo they perform the same physiological activities f

Laboratory exercise. Study of an amoeba (amoibos — changing). The
amoebas belong to the branch of animals called Protozoa (protos — first ; zoon —
animal : first or early animal). To locate amoebas, scrape the undersurface of
the leaves of Elodea on to a glass slide. Add a drop of water and cover with a
cover glass. Another method for finding amoebas is to crush some pond lilies
or other water plants and let the mass remain undisturbed for a few weeks.
Tiny animals will usually be found in the scum which forms. Mount some of
the scum and locate an amoeba with low power, then study it with high
power. Later stain with iodine and again observe.

I. Describe the amoeba, including shape, color, and number of cells.

II. How does its shape differ from any cell previously observed? The
irregular projections of protoplasm are called pseudopodia or pseudopods
(pseudo — false; podium — foot). What seems to be the function of the
pseudopodia or false feet ?

III. Describe the movement of the animal. Suggest a reason for the
name amoeba.

IV. After staining it with iodine, find cytoplasm, nucleus, * and a space
called the contractile vacuole. The clear outer protoplasm of the cell is called
ectoplasm and the granular inner area is endoplasm.

V. State three structures found in the Spirogyra not found in the amoeba,
and one structure found in the amoeba not found in the Spirogyra.

VI. State a difference in nutrition between Spirogyra and amoeba.

LIFE FUNCTIONS OF AN AMOEBA

VII. Name a function performed by the amoeba that the green cell cannot
perform. What is the value of this function to an animal organism ?

VIII. Make a drawing three inches in diameter, of an amoeba, and label
cytoplasm, nucleus, plasma membrane, pseudopodia, and vacuole.

Life functions of an amoeba. Ingestion. When an amoeba
comes in contact with a particle of food, it throws out pseudopo-
dia which flow over and around the food. The food particle is then
taken into the cytoplasm. This engulfing of food by the amoeba
is its method of food getting, or ingestion. The amoeba shows little
power of selection of food. It takes in almost anything small enough
to be engulfed. The cytoplasm encloses the food and forms a vac-
uole or bubble encircled by plasma membrane. The food and
some fluid deposited by the cytoplasm are inside the vacuole.

Digestion. The engulfed food is principally smaller microor-
ganisms and particles of plants. These consist of combinations of
the nutrients, proteins, fats, and carbohydrates. The particles cir-
culate in the streaming cytoplasm in the form of a food vacuole.
The cytoplasm secretes aw

5 ^. r ^4n3k>pWm/

Xp*eu2topdcl

nt-ccletxs

contractile
>< : vacuole

digestive enzymes to con-
vert these nutrients into a
soluble form which can
then be assimilated by the
protoplasm. As the circu-
lating protoplasm carries
the food around the cell,
the digestive enzymes, pro-
tease, lipase, and amylase,
gradually dissolve the nu-
trients in the food. These
nutrients pass through the
plasma membrane of the vacuole by osmosis and mingle with
the cytoplasm. The indigestible materials that have entered with
the food may be eliminated from any part of the organism.

Amoeba may assume a variety of shapes. Compare
the animals you studied under the microscope with
these diagrams.

TYPICAL ANIMAL CELL

Assimilation. The digested protein together with water and
absorbed mineral matter are converted into protoplasm by the ac-
tivity of the cytoplasm of the
living amoeba. This is as-
similation. As a result of as-
similation, new protoplasm is
formed and the animal grows.
Respiration. Oxygen from
the air in the water may
enter through any part of the
surface of the amoeba. It
meets the digested nutrients
in the cytoplasm and oxida-
tion takes place, that is, oxy-
gen combines with carbon and
hydrogen compounds. As a
result of oxidation, energy is
released. This energy en-
ables the amoeba to carry on
its functions. Since protein, fat, and sugar contain carbon and
hydrogen, carbon dioxide and water are oxidation products.
Protein gives rise to nitrogen, sulphur, and phosphorus products,
also, one of which, urea, is a nitrogenous waste. The wastes
resulting from oxidation are collected in the contractile vacuole.
This bursts and expels the wastes through the plasma membrane
into the surrounding water.

Reproduction. When the amoeba reaches a certain maximum
size natural to its species, the nucleus divides in two parts and
then the entire cell cleaves in two equal parts. This results in the
production of two distinct cells each with its own nucleus. This
process is called reproduction by fission.

Irritability. The amoeba is very sensitive to outside stimuli.
If it is touched with a pointed object, it draws away. It moves

A patient investigator watched and described
the behavior of an amoeba as it went after a
spherical food particle which had rolled away.
The drawing shows how the amoeba pursued and
engulfed the particle of food.

IRRITABILITY

from the object by sending out tiny projections of cytoplasm,
which are known as pseudopodia.

If an amoeba comes in contact with food, it surrounds the
particles. If touched with wires carrying an electrical charge, it
rolls itself up into a ball as if shocked. It shows no activity at
freezing temperature, and it evidences the greatest activity at a
temperature of about 85° F. It will become spherical, hard, and
lifeless in very hot water. If a beam of light is directed toward
one side, the amoeba will move away from the light and toward
the darkened portion. If a grain of sugar is placed in a drop
of water, the amoeba will move toward the sugar ; if a grain of
salt is placed there, it will move away. If, with a very fine
pipette, a chemical is injected into the amoeba's cytoplasm, the
animal is able to sever off almost immediately that part of the
cytoplasm and will move from the rejected part as quickly as
possible. Recently, Dr. R. H. Chambers has developed methods
of micro-dissection. By means of a microscope and a set of tiny
dissection instruments and capillary pipettes he can dissect or
inject chemicals in or near specimens while they are mounted under
the microscope.

The responses or activities of the amoeba called forth by stimuli,
are tropisms (tropos — a turning) . These responses may be toward

When the amoeba reaches its maximum size, the nucleus elongates and divides into two nuclei.
The animal constricts and breaks apart into two daughter cells, each with one nucleus.

the stimulus, in which case the tropism is called a positive tropism
and designated by a plus sign ( + tropism). If the resulting ac-
tivity is a motion away from the stimulus, the tropism is con-

TYPICAL ANIMAL CELL

sidered negative and is represented by a minus sign ( — tropism).
The different tropisms are named in terms of the stimulus to
which the organism is reacting. Listed below are the tropisms

shown by the amoeba.

Photo tropism — reaction to light.
Chemotropism — reaction to
chemicals.

Thigmotropism — reaction to
touch or contact.

Thermotropism — reaction to
heat.

Galvanotropism — reaction to
electric current.

These reactions are largely pro-
tective. As a result of tropisms
the amoeba often escapes unfavor-
able conditions and gets into an
environment where the conditions
are favorable for its life and ac-
tivity.

Locomotion. By means of its
pseudopodia, the amoeba " walks"
from place to place. It sends out
a stream of protoplasm in one
direction. Gradually the rest of the cytoplasm carrying the
nucleus flows into it ; and again a thin stream is sent out. Thus
the organism moves. By means of the function of locomotion it
can get food and escape unfavorable conditions.

Problem. Study of a Paramecium.

Place some hay in a beaker of distilled water. Heat in order to soften the
hay. Let the material stand two or three weeks. The addition of a little
thyroid extract will usually promote the multiplication and growth of the
organisms present. This is a Paramecium culture.

When the amoeba is viewed from the
side, pseudopodia may be seen to ex-
tend which result in movements like
walking.

LOCOMOTION 47

I. Take a drop of the infusion, place it on a slide and cover with a cover
glass. The microorganisms called Paramecia should be present.

A. Describe the cellular structure of a Paramecium.

B. How does its movement differ from that of the amoeba ?

C. What proof have you that the Paramecium is cylindrical and not flat ?

D. Describe the shape of a Paramecium. The end that goes forward
most of the time is called the anterior end. The opposite end is the pos-
terior end. Describe the shape of the anterior and posterior ends.

II. Put a few threads of cotton or some finely shredded lens paper on a
glass slide. Place on this a drop of the Paramecium culture and focus under
the low power.

A. Describe the appearance of the threads of cotton under the microscope.
What effect do the threads of cotton seem to have on the movement of
the Paramecium ?

B. Note the furrow in one side of the animal. This is called the groove.
At the base of the groove is a mouth, and the cylindrical structure below
is the gullet.

C. Look closely at the plasma membrane. The structures that you
should observe there, are projections of protoplasm and are called cilia.
Describe any movements of the cilia. Suggest a function of the cilia.

D. The groove and gullet are also lined with cilia. Suggest a function
for these cilia.

E. At either end of the Paramecium you will see a small clear bubble.
Watch each bubble form, grow larger, and burst. These are the contractile
vacuoles.

III. Stain the Paramecium with dilute iodine and mount under the low and
high power. What evidence of ectoplasm and endoplasm can be seen? De-
scribe a difference between these two kinds of protoplasm.

IV. Take a new culture and add a small amount of blue fountain pen ink
to it, and again put a few threads of cotton on it.

A. Focus under the high power. Observe the long hairlike structures
that are thrown out. These are protective structures of offense and defense
called trichocysts.

B. Observe the two nuclei. The larger nucleus is called the macro-
nucleus (makros — large) and the smaller, the micronucleus (mikros —
small). It may be necessary to stain the specimen with iodine to see these.

C. Draw a Paramecium three inches long and label all the structures
observed.

D. Write a brief description of the Paramecium.

TYPICAL ANIMAL CELL

The physiological functions of the Paramecium are somewhat
more complex than those of the amoeba because of the increasing
complexity of structure.

Nutrition. Bacteria and any other tiny plants or protozoa that
are small enough are swept by the current created by the cilia

into the oral groove. These
are driven through the gul-
let, where they are made
into a food ball and dis-
charged into the cytoplasm
of the cell. The food ball
is carried around as a vac-
uole by the streaming cyto-
plasm. The processes of
digestion, circulation, as-
similation, growth, and res-
piration in the animal are
similar to those described
for the amoeba. As the
food is gradually digested,
any material that cannot be
digested is collected at a
certain small area of the
plasma membrane in the
posterior end of the animal.
The membrane breaks at
regular intervals to throw
off the solid food wastes.
This mechanism is called
the anal opening. Because
the wall always breaks in
the same region to let out the solid material, it is frequently called
a weak spot. The wastes, carbon dioxide, water, and urea, formed

cilioc

triehocysts

ec/toplcrsm
en&oplccsm
. jp«lliole>

llnicronucletrs

oral groove.

^oo*3L vaduole*

v. corn. o. I.
spot.

srcmal

Note in this diagram the structures that you were
unable to see in your microscopic study of the Para-
mecium.

LOCOMOTION

in the oxidation process, are collected by tiny radiating canals
and emptied into a central contractile vacuole at each end of the
organism. When these vacuoles have attained a certain size, the
cytoplasm . surrounding them contracts and discharges the wastes
through the cell membrane. The contractile vacuole is constantly
filling and discharging.

Locomotion. Cytoplasmic structures called cilia project through
the cell membrane, and, by rapidly lashing back and forth, propel
the animal through the water. The cilia are ar-
ranged in rows all over the body. All the cilia in
a row beat at the same time. If, with a needle,
the thread of cytoplasm which controls the beating
of a row of cilia be cut, the entire row will cease to
beat and remains paralyzed. Due to the more
rapid beating of the cilia in the groove, the animal
rotates and proceeds in a spiral rather than a
straight path. It usually progresses with the blunt
or anterior end forward, but can reverse its cilia
and travel equally well with the pointed end for-
ward. Such a reversion often takes place when it
meets an obstacle. If confined in close quarters,
the Paramecium can pass through small openings
due to the elasticity of its body.

Reproduction. Reproduction occurs by fission,
as in amoeba. Each of the two nuclei divides and
each daughter cell contains a macronucleus and
micronucleus. A new groove and gullet are formed
in one of the cells and two new contractile vacu-
oles appear. When cell division or binary fission goes on indefi-
nitely, the cells sometimes lose their vitality. When this happens
they become smaller, and, in some cases, distorted. Under such
conditions, two Paramecia come together. The cell membranes
are dissolved at the point of contact and a bridge of cytoplasm

A Paramecium
reaches a maximum
size. The two nu-
clei elongate, a con-
striction appears,
and the two daugh-
ter cells split apart.
This is reproduc-
tion by fission.

50 TYPICAL ANIMAL CELL

is formed. The macronuclei disappear and the micronucleus goes
through a series of complicated divisions. Finally one part of the
nucleus of each cell passes over the cytoplasmic bridge and unites
with a part of the micronucleus in the opposite cell. The animals
then separate and there is a reorganization of parts to restore the
structure to the normal state. This exchange and union of nuclei
is called conjugation. The process seems to give the Paramecia
renewed vigor and vitality. The cells may now go on dividing for
hundreds of generations before conjugation again takes place.

It has been shown by one scientist that the lowered vitality of
a colony of certain Paramecia may be caused by the 1 surrounding
media of their environment. If this becomes concentrated with
wastes or materials that are unfavorable, conjugation may occur.
On the other hand, if careful control is kept of this material in which
the creatures live, and if abundant food is supplied and wastes
removed, certain Paramecia will divide generation after generation
without resorting to conjugation. L. L. Woodruff, a professor at
Yale University, has kept a strain of Paramecia active for several
years. Thousands of generations have been produced from the
creature with which he started. By exercising great care to make

the surroundings most health-
ful for Paramecia, he has pro-
Pellicle - duced these thousands of gen-
erations without having them
conjugate or die. This biolo-
SSoagulcctecl Protoplasm, gist believes that if conditions
ohoi is added to a Paramecium the proto- are carefully safeguarded and

plasm is dehydrated, the strands of cytoplasm, controlled, these tinV masses of
cilia, are pulled through the cell membrane or "
pellicle leaving the rows of openings in the protoplasm known as Para-
pellicle. r . .

mecia will live forever.
Irritability. The reaction of Paramecia to external stimuli is
much the same as in amoebas. Because of their cilia, they can
respond more quickly toward or away from stimuli. They have a

PROTOPLASM IS SPECIALIZED

special set of protective structures called trichocysts. Each one
of these structures consists of a pocket fitted with a long strand of
cytoplasm which is thrown out when danger is near. This strand
secretes a poisonous substance.
The whole mechanism acts as
a protection. A worm, much
larger than a Paramecium, as
it thrashes about, might injure
the Paramecium. To protect
itself, the Paramecium dis-
charges trichocysts which will
pierce or poison the enemy so
that it will become inactive.

Protoplasm is specialized.
The specialization of protoplasm
in Paramecium is a step toward
the specialized organs for defi-
nite functions found in higher
animals. The protoplasm of
the amoeba shows very little differentiation. Pseudopodia may be
thrown out from the body at any place. Food may be taken in and
water given off from any part of the body. The only specialized
protoplasm of the amoeba seems to be the nucleus and the plasma
membrane around the contractile vacuole. In the Paramecium
there are definite parts of cytoplasm specialized to form cilia.
These are constant structures used for locomotion and for propel-
ling food into the mouth. There is a definite part of the cytoplasm
forming the groove, mouth, and gullet. Food is taken in through
these structures. The two nuclei, the contractile vacuoles, cell
membrane, and anal canal are all fitted or adapted to the functions
they have to perform. The Paramecium is one of the simplest
organisms to show definite adaptations to function. Physiological
division of labor is accomplished by specialized protoplasm.

■Trichocysts

If a small drop of fountain pen ink is put on
a Paramecium, the animal throws out long
protoplasmic structures, trichocysts. These A
threads usually secrete a substance that stuns '*-
an enemy or the prey.

52 TYPICAL ANIMAL CELL

Simple animals are very similar to simple plants in structure and
function. The main differences are that animals have the function
of locomotion, and are adapted to perform this function. Very few
plants have the power of locomotion. Green plants manufacture
their own food by means of their chlorophyll, and do not have to
seek food as most animals do. In addition to the plasma mem-
brane, there is a protective wall in the plant cells made of a non-
living material, cellulose. This is missing in animal cells. Amoebas
are bounded by the plasma membrane only.

A cell, either plant or animal, has been shown to be a tiny mass
of protoplasm, generally having a nucleus and having a boundary,
a cell wall, or an animal membrane. The cell theory as first stated
by Schleiden and Schwann has been checked by many scientists
over a long period of years. To-day, it is no longer considered
a theory but is accepted, somewhat modified, as a doctrine.
Among other things this theory states that the cell is the unit of
structure and of function and that all plants and animals are
made up of cells and cell products.

Questions

1. Name the forms of energy needed by the amoeba or Para-
mecium.

2. Classify the physiological functions into nutritive, adaptive, and
reproductive. Give the functions of each class.

3. Why is digestion necessary in animals ; in plants ?

4. What is the main difference in the nutrition of a plant and
animal ?

5. Discuss some positive and negative examples of tropisms.

6. In outline form, compare the structure and function of a one-
celled plant and a one-celled animal.

7. Discuss the importance of chlorophyll to animals.

8. What is meant by physiological division of labor and speciali-
zation of protoplasm ?

9. Make a library report on the economic importance of protozoa.

p^O?

(

When cells divide

CHAPTER VII

THE RESTING

AND
DIVIDING CELL

the surface area increases.

What is the nature of protoplasm? What progress has been made
in the building of protoplasm in the laboratory? Are the functions of
the cell related to the functions of the organism in any specific way?

All living things are made of cells. The cell is the unit of struc-
ture of the. Protozoa. Higher forms of organisms are composed of
many cells. It is impossible to discuss the functions of higher
organisms without referring to the cell in some detail, for it is
really the cells of the organism that perform these functions. Cells
vary in shape, size, and structure, but they are all alike in consist-
ing of a mass of protoplasm usually containing a nucleus, and
always surrounded by a plasma membrane. A plant cell is in-
closed in a cell wall which usually consists of cellulose, a form of
carbohydrate. Cells are either in a state of division, or, if not
actively dividing, are said to be in a state of rest. When in the so-
called state of rest, activities other than cell division are being
carried on in the cell.

The nature of the cell and its make up. So complex is the cell
and so much has been written about it that there is now a whole
branch of biology, cytology, concerned with cell investigations.

Cytologists differ as to the detailed structure of protoplasm.
Some think it is composed of an extremely minute network of fibers,
similar in appearance to a sponge, inclosing a liquid. This is

THE RESTING AND DIVIDING CELL

called the reticular theory. A second group of scientists believes
that protoplasm is similar to a mass of bubbles, like soapsuds or a
froth. This group thinks the so-called fibers are only the delicate

(TrccriuXaf
".structure

r^tioulotr
Structure

cclveolcc**
structure

The structure of protoplasm has not been satisfactorily determined. It has been described in
various ways and represented as in the above diagrams.

lines separating the bubbles from each other. This theory is called
the alveolar or the foam theory. A third group thinks that proto-
plasm is an infinite number of very small, living, moving granules
arranged in lines resembling fibers. These fibers, differently ar-
ranged, make various figures This is the granular theory. All
biological problems are centered in the cell, including the manu-
facture and use of food, and an understanding of the nature of
and the control of problems of heredity. Such problems shall
never be satisfactorily settled until more knowledge of the work
of the cell is gained.

Many investigators are now trying to solve cell problems. Con-
sider the work of Alexis Carrell, the French surgeon. For years
he and his assistants have been working at Rockefeller Institute,
New York city, trying to develop various cells outside of a living
organism. For sixteen years he has kept cells of a chicken embryo
actively growing. He has also succeeded in getting other living
cells to grow under controlled circumstances. He has been able to
use some of these cultivated cells to try out the effects of various
antiseptics. It is possible that cultivated tissues will be of great
value in operations of skin grafting. Growing tissues for this
purpose is only one small part of the work now being done by
Carrell. He has transplanted whole organs from one animal to

CHARACTERISTICS OF PROTOPLASM 55

another and succeeded in having them grow and function in the
second animal. His work on antiseptics, during the World War,
was invaluable. It seemed almost impossible to keep wounds free
from contaminating germs which destroyed the cells. He and
Dakin prepared and introduced an antiseptic, Dakin solution, for
treating wounds. This solution, which did not injure the tissue,
saved many soldiers from gangrene and other infections.

The problem of heredity which involves an understanding of
certain cells is now being studied by many scientists. It is a well
known fact that certain physical and mental traits are transmitted
from parent to offspring through a granular material, chromatin,
found in the nucleus of the germ cells. This chromatin combines
to form the structures, chromosomes, which carry and transmit
certain character determiners. Experiments are now being made
to find out exactly what characters are inherited, and the amount
of the hereditary-bearing substance. Why has a certain individual
one ability, while another in the same family lacks this ability?
Scientists, including T. H. Morgan, W. J. V. Osterhout, E. B.
Wilson, and R. H. Chambers, are working on this problem at the
present time.

Characteristics of protoplasm. Protoplasm is being studied by
many biologists from four different viewpoints.

Physically — it is a constantly streaming, colorless, slimy, semi-
liquid substance similar to the white of an egg. It is a colloid.
By that we mean it is a mass of tiny solid particles suspended
in a liquid. It will not pass through a parchment membrane.

Chemically — it is a very complex unstable mass made of pro-
teins and inorganic salts associated with a large amount of water
and frequently containing carbohydrates and fats.

Structurally — it is variable. Sometimes it appears purely gran-
ular, other times fibrillar or threadlike, and again it may resemble
a mass of foam or bubbles. It varies according to the activity
and individual nature of the cell.

THE RESTING AND DIVIDING CELL

Physiologically — it lives, moves, reproduces, and dies. If kept
under proper conditions, such as Woodruff and Carrell kept it in

their experiments, protoplasm seems
to be able to live indefinitely.

Dr. Calkins, of Columbia Uni-
versity, has performed many experi-
ments on certain cells to show
the importance of the presence of
nuclear material. In one experi-
ment he used Uronychia, a one-
celled animal. Like its relative,
Paramecium, this creature has two
nuclei, a macronucleus and a micro-
nucleus. The protozoologist divided the tiny creature into two
fragments, each having an equal part of the macronucleus and
micronucleus. Both parts healed. Both grew and reproduced.
Then he divided a second organism unequally so that the smaller

BUeS

An amoeba was cut apart, one portion
bearing the nucleus. Both fragments
healed, both continued to move, but the
one without a nucleus soon slowed down,
came to rest, and died. The nucleated
portion grew and became a normal
amoeba.

A Stentor, relative of Paramecium, was
cut in three parts. Each fragment had a
part of the nucleus. Each grew and re-
generated missing parts, resulting in three
new and complete animals.

A Stylonychia was cut so that only one of
three fragments contained nuclear material.
All three swam about for a time but only the
portion bearing the nuclear material regen-
erated lost parts, grew and reproduced.

part had little macronuclear material and no micronucleus. It
took in little food, grew, but did not reproduce. It soon died.
The larger portion of the animal, containing most of the macro-

FUNCTIONS OF DIFFERENT PARTS OF PROTOPLASM 57

nucleus and the micronucleus, healed, took in food, grew, repro-
duced, and was soon a normal animal.

Many other similar experiments have been conducted, the results
of which indicate that the macronucleus is an essential factor in the
metabolism, growth, and regeneration of the organism. The micro-
nucleus has to do with reproduction.

The protoplasm may be divided into cytoplasm and nucleo-
plasm.

Structures found in cytoplasm Structures found in nucleoplasm

Cell wall (plant cells only) Nuclear membrane

Plasma membrane Nucleolus

Vacuole Chromatin granules

Cell sap Linin network

Vacuolar membrane Nuclear sap

Chloroplasts (in some cells)

Starch grains

Crystals (protein, urea)

Centrosome (animal cells chiefly)

The functions of the different parts of protoplasm. The nucleus
consists of very dense protoplasm bounded by a delicate membrane.
It may lie anywhere in the cytoplasm of the cell. In fact, it is
constantly being carried to different parts of the cell by the stream-
ing movements of the cytoplasm. It generally contains a minute
spherical body, the nucleolus. Sometimes there are several nucleoli
in one cell. The exact function of the nucleolus is not known.

A typical resting nucleus shows many particles called chromatin
granules. These are enmeshed in a network called linin. The
chromatin granules are believed to be the carriers of hereditary
character determiners; such as, the color of a person's eyes, his
disposition, his height, or his artistic ability. These particles are
able to absorb certain stains more readily than the rest of the
materials found in the cell.

The nucleus controls the work of the cell. It is the center of all
the physiological activities of the cell; such as, nutrition, respiration,

WH. FITZ. AD. BIO. 5

THE RESTING AND DIVIDING CELL

cell ^rctll

plcc5m.cc
membrctrxe.

ntccleohjus.
rcxjcelevca.

Cytoplasm
vctcuole.

A plant cell has a cell wall. When viewed
through a microscope large vacuoles are generally
seen in the cytoplasm.

growth, and reproduction. A cell without a nucleus (the nucleus
having been removed with a tiny knife) will not live. Without a
nucleus, although food is present, the cell cannot take in food, nor

use food, and its respiration
becomes greatly reduced.

The cytoplasm is the living
material of the cell, surround-
ing the nucleus. It is semi-
fluid, less dense than the
nucleoplasm, and is always
in motion throughout the cell.
The cell wall is found as
an additional bounding layer
around plant cells. It is com-
posed of a substance, cellulose,
which has the elements found
in starch ; namely, carbon, hydrogen, and oxygen. Cytoplasmic
threads penetrate into the cell wall, and cause it to grow in thick-
ness by depositing woody material. As the cell gets older, more
and more woody material is deposited. Within this thickened
wall of the plant cell is the plasma membrane. In the animal cell
the plasma membrane is the only bounding layer; it lacks the
material which makes up the plant cell wall. The plasma mem-
brane is a very delicate layer of dense cytoplasm and has three
functions in plants and animals. It regulates osmosis by permit-
ting the entrance of needed materials. It determines the shape or
form of the cell. It affords protection against loss of water.

A vacuole is a space in a plant cell which becomes filled with a
liquid called the cell sap. The cell sap contains a little dissolved
sugar, mineral salts, crystals (waste and storage products of the
plant cell), and a great deal of water. The presence of a vacuole
helps the plant cell to swell up and become very large even
though only a small amount of cytoplasm is present. This cyto-

FUNCTIONS OF PROTOPLASM

plasm becomes stretched into a thin layer around the vacuole.
The vacuole is bounded by a delicate layer of cytoplasm, J;he
vacuolar membrane. Some animal cells possess vacuoles similar
to the food and water vacuoles of the protozoans, and contractile
vacuoles for the excretion of nitrogenous wastes.

A chloroplast is a small mass of cytoplasm, colored green by
the chlorophyll pigment. The cell aided by this chlorophyll in the
presence of sunlight is able to manufacture raw materials into the
food necessary to build protoplasm.

The centrosomes are the foci for the starlike formations ap-
pearing like fibers of cytoplasm. These seem to be of great
importance in the division of the animal cell.

The sum total of all the functions of the cell is called metabolism.
It refers to the physiological activities of all living protoplasm.
There are two kinds of metabolic activity ; anabolism and katab-
olism. When the physiological activities tend to build up proto-
plasm, they are termed anabolic. Two examples of anabolic

celt „
membrane

ceritrosotrrcl

nuclear
membrane

chromatin

nucleolus

-nucleus

cytoplasm
jplastiB,-

vacuole<AjQ>;

Compare this animal cell with the plant cell on the previous page.

activities are starch making and assimilation. When these pro-
cesses tend to break down protoplasm, they are katabolic. An
example of a katabolic process is the oxidation of food. Both types

THE RESTING AND DIVIDING CELL

of processes are essential to the work of the cell and depend upon
each other. The anabolic activities are concerned chiefly with
nutrition and the katabolic, with energy release. For example,
in order to perform the anabolic functions of assimilation', the
cell is dependent on the energy derived from the katabolic func-
tion of respiration.

Ingestion

Digestion

Absorption

Circulation

Assimilation

Nutrition

Growth

Secretion

Reproduction

Respiration
Irritability
Excretion
Motion

Anabolism

Katabolism

Metabolism

Cell division. When a cell is not at rest, it is in a state of divi-
sion. There are two methods of division: 1. Direct division —
also called amitosis {a — without; mitos — thread), and 2. in-
direct division or mitosis. In amitosis, direct division, the nu-
cleus simply pinches in half and becomes separated into two
daughter nuclei. The cytoplasm sometimes cleaves and a part
goes with each nucleus. * This sort of division takes place only in
cells which are very active and need very many nuclei in the work
they are doing. Amitosis may also occur when cells have been
very active, and the nucleus, becoming exhausted, multiplies
rapidly by breaking into fragments.

Mitosis or indirect cell division. Mitosis is a very compli-
cated process when compared with amitosis. The nucleus lives a
very long time in an active and young cell, and will divide a great
many times. Each time the nucleus divides, the entire cell di-
vides, forming two new cells. Each cell will have exactly the

MITOSIS OR INDIRECT NUCLEAR DIVISION

same characteristics possessed by the original cell. This equal
inheritance is made possible by the dividing of every chromatin

1 2 3f 4r

Anaphase

felopliccse

Mitosis of an animal cell, Ascaris egg. Follow the stages shown in the diagram with the
description given in the text.

granule into two parts, so that each cell will possess the same
number. In order to bring about equal splitting, several distinct
stages are gone through. This process takes place in all plant
and animal cells, from the protozoans and algae to the cells of the
largest trees and the most complex animal, man.

In many animal cells, the first sign of mitotic activity is the
separation of the centrosome into two parts connected by delicate
fibers. Around each center, groups of fibers radiate, causing the
structures to look like stars. Hence, they are called asters and
the radiating rays are known as astral rays.

The centrosomes move further apart around the nuclear mem-
brane and the spindle threads become longer. At the same time
the chromatin granules become arranged in the form of separate
threads or a continuous coiled thread, the spireme.

THE RESTING AND DIVIDING CELL

The spireme breaks up into a number of parts called chromosomes.
Each plant or animal cell seems to have a definite number of these.

In the cells of human beings,
the spireme breaks up into
forty-eight chromosomes. In
the onion cell, there are sixteen.
In a certain little fruit fly,
there are only eight. These
numbers are always constant
for a particular species. Four
chromosomes are shown in the
diagrams (page 61) illustrat-
ing mitosis of an animal cell.
The asters separate more
Photomicrograph of a section of a growing and more widely causing the

root tip of an onion. How many different stages £U~„~ U~+ w ~~.^ +U~ + U~

of ceil division can you identify? fibers between them to be-

come longer and to assume
a spindlelike shape. Finally they reach the opposite sides of
the nucleus. The chromosomes are' now drawn into the central
part of the spindle forming a ring around it, in a plane called
the equatorial plate. All of these changes are a part of the
prophase stage (beginning) of mitosis. The prophase ends with
the chromosomes arranged on the spindle in the equatorial plate.
Each chromosome now splits lengthwise into exactly two similar
parts. The actual splitting of the chromosomes may occur before
the arrangement at the equatorial plate. Division of the chromo-
somes has been accomplished. This is the metaphase (middle)
stage of mitosis.

The split chromosomes begin to separate and move toward
the centrosomes or the poles. As they approach their poles the
chromosomes lose their regularity of outline, and upon reaching
the poles each group becomes converted into two new nuclei.
This is the anaphase (approaching the end) stage of mitosis.

MITOSIS OR INDIRECT NUCLEAR DIVISION

Mitosis ends with the telophase. A new cell wall forms on the
spindle, midway between the two daughter nuclei. It divides
the cell into two parts, in each of which a nucleolus now appears.

Problem. Study of mitosis. Study of pre/pared slides of Ascaris
under the microscope.

I. Select a good example of the anaphase stage.

A. How does the slide differ from the diagrammatic drawings ?

B. What causes you to identify it as an anaphase stage ?

II. Identify any other stage of mitosis present in your specimen.

III. Make an outline drawing of three different cells seen through the micro-
scope.

IV. Alongside of each drawing, copy and label the diagram of the phase
which most nearly resembles the viewed cell.

A very similar process takes place in plant cells. Centrosomes
are lacking. The spindle forms from material which is probably of

A group of cells of a plant showing various stages in the mitotic division of the cells. Com-
pare and contrast this series with the diagrams showing mitosis of an animal cell.

THE RESTING AND DIVIDING CELL

nuclear origin. A cleavage plate through the middle of the cell is
secreted by the cytoplasm. This divides the cell into two parts.
There is no constriction here as there was in animal cells.

Cell theory. The illustration (below) shows some of the men
who have discovered and made known many interesting facts about
animal and plant cells, so that we to-day have come to have four
ideas concerning the cellular structure of all organisms.

1. The cell is the unit of structure of all living plants and animals.

2. The cell is the unit of all physiological functions of living plants
and animals. It is the cell that breathes, digests food, excretes wastes,
moves, and performs all the other physiological functions.

3. The cell embraces all the hereditary qualities of the organism
within its nuclear membrane.

4. Plants and animals may consist of single cells. They always
start with a single cell, and in their early stages of development (em-
bryo) this cell divides and changes into many cells.

Questions

Hall of Fame for biologists -who worked on cell*

Century . .

Country . .

Contributions

1. Copy the names and fill in the blank spaces in the above table.
Check your results with your answer to question 1 on page 33.
...2, By means of paraffin, soap, clay, or plasticine try to make
models of a resting cell and some of the stages of mitosis. . . , '-.

SUPPLEMENTARY READING 65

3. Name the structures common to both plant and animal cells.

4. List the living and nonliving structures in a plant cell.

5. What parts of a cell are most active during mitosis ?

6. In what kinds of cells is amitosis carried on ? Why ?

7. Draw, a characteristic stage of each phase of mitosis.

8. Why is it that every cell in an organism has chromosomes of the
same nature found in every other cell ?

9. Discuss the cell as the unit of structure ; the unit of function.
10. Discuss the importance of the cell in the development of the

individual.

Supplementary Reading

Gager, C. S., General Botany (P. Blakiston's Son & Co.).

Locy, W. A., Biology and Its Makers (Henry Holt & Co.).

Wilson, Edmund B., Cell in Development and Heredity (The Macmillan Co.).

CHAPTER VIII

STRUCTURE OF
HIGHER PLANTS

Photomicrograph of corn
stem.

Photomicrograph of woody
stem.

What is meant by physiological division of labor? Does each plant
cell of a higher plant live independently or are the cells dependent
on each other? Why can one type of cell perform a function better
than another type? What advantages have higher plants over simpler?

Social division of labor. In any civilized community certain
individuals perform one type of labor more efficiently than others.
There are seamstresses to make clothes, shoemakers to make shoes,
milliners to make hats, engineers to run trains, clerks to perform
clerical work, typists to typewrite, and numerous other specialists,
each performing a specific work. The people who are most suc-
cessful are those who are particularly fitted or adapted for their
positions, either through special training, natural talent, or size.
More efficient work is accomplished in less time when it is divided
among specialists than if each man had to do all the work himself.
Similar to the division of labor among people in the industrial
world, there are in our bodies numerous activities that are car-
ried on by various structures especially adapted for that work.

Physiological division of labor. There is physiological division
of labor in all plants and animals. The amoeba, Paramecium,
Pleurococcus, Spirogyra, and countless other plants and animals
are sufficient each in itself. Each with its one cell, by means of
specialized protoplasm, performs all the activities and processes

PHYSIOLOGICAL DIVISION OF LABOR 67

necessary for living. These organisms, however, live very simply.
The many-celled plants and animals are much more complex.
They consist of a variety of cells. Differentiation of cells and
greater specialization of function are shown in these. Whenever
there is a collection of similar cells in higher organisms, it is known
as a tissue.

Problem. Study of the lower epidermis of a leaf.
Peal off the under surface of a geranium leaf. Mount it under the low
power of the microscope.

I. Describe the shape, color, and structure of the different types of cells
in the epidermis.

A. Epidermal cells have unusually thick walls. Remembering that the
epidermis is the outer layer of the leaf, suggest a function of the thick-
walled cells.

II. Note the small holes between the oval-shaped cells. Each of these is a
stoma (from a Greek word meaning mouth or opening). Suggest a function for
these openings or stomata.

A. The oval-shaped cells, called guard cells, are so constructed as to
cause the opening and closing of the stomata.

B. Draw and label the lower epidermis of a leaf.

C. Describe briefly the functions of the cells and the adaptations of the
cells to their functions.

Problem. Study of a cross section of the same leaf.
Place a leaf between two pieces of cork and cut through the cork with a
sharp razor blade.

I. Describe the general arrangement of the cells in the upper epidermis,
middle area, and lower epidermis of the leaf, as seen in the cross section.

II. Note the upper colorless epidermal cells bearing hair-like structures.
Suggest a use for these cells.

III. Note the regular arrangement of the cells immediately under the
upper epidermis. This layer is called the 'palisade layer or tissue. How
are the cells in the palisade layer arranged so as to secure sunlight ?

IV. Observe the loose arrangement of the cells under the palisade tissue.
These cells form the spongy layer.

A. What is the advantage of the air spaces among the green cells?

B. State a function of the green cells of the leaves.

68 STRUCTURE OF HIGHER PLANTS

V. Observe the side view of the cells in the lower epidermis. Describe the
appearance of the epidermal cells, guard cells, and stomata.

VI. Discuss the importance of the translucent character of the epidermal
cells.

VII. What specialization of structure for function is shown in a green leaf ?
Give at least five examples.

VIII. Secure two leaves from a rubber plant. Coat the upper epidermis of
one and the lower epidermis of the other with vaseline. Seal the ends of the
stems with vaseline. Keep them in a cool place for several days.

A. State your observations.

B. . Suggest a second use for the stomata.

Problem. Study of the vascular and supporting tissues in a leaf.

Break off a narcissus leaf and separate some tissues from the broken end.
Mount on a glass slide.

I. Observe some of the cells with spiral thickenings on the walls. These
are tracheids (xylem). In order to keep open the passageway of the tubes
formed by these cells, spiral thickenings of wood form on the wall. Originally,
there were cross walls where one cell ended and another began, but the parti-
tions have been absorbed, leaving an uninterrupted canal. Water travels
up through these tracheids.

II. There are other cells with sievelike plates at regular intervals. These
are the sieve tubes (phloem). Through these structures materials pass down
the plant from the leaves to the roots.

A. Trace a material that travels from leaves to roots.

B. Why do materials tend to pass more quickly down than up ?

C. What is a possible advantage of the sievelike cross walls in the
sieve tubes? Each sieve tube is a single row of elongated cells placed
end to end and the thickened end walls of these cells have numerous
perforations.

III. There are also supporting tissues called wood fibers that have very thick
walls of cellulose. Some of them consist entirely of cellulose and compose the
supporting structure in a plant.

IV. Place the roots of a complete narcissus plant or any other young plant
in red ink or eosin in order to show the continuous pathway from roots to leaves.

A . What evidence of the passage of fluids do you observe ?

B. Trace the liquid that travels up in a plant from the point of en-
trance to the cells that use it. . " j

V. Draw and label as many of the tissues as you have observed;

SPECIALIZATION IN HIGHER PLANTS

VI. In a paragraph, discuss the functions of the vascular or conducting and
supporting systems of a plant, including the adaptations or specializations for
various functions.

upper surface lower surface

Most leaves are covered with a layer or layers of thick-walled cells lacking chlorophyll.
The lower surface of most leaves bears certain paired cells containing chloroplasts. These
cells permit the passage of substances in and out the leaf. They are the guard cells.

Specialization in higher plants. Higher plants perform all
the physiological functions necessary for life. Each individual
cell performs many of these same functions, but at the same time
each cell is adapted to perform

one function better than others.
Absorption of water and minerals
is performed by special epidermal
cells called root hairs, found on
the roots. These cells are long
and slender and grow among the
particles of soil. The water and
mineral matter pass through the
root hairs, then through other
root cells until they reach the
ducts (xylem) near the center of
the root. By means of capillary
action, evaporation of water from
the leaves, and the pressure of
other fluids following, the water
rises in the spirally-thickened

chloroplasts

wall of a
guaro. cell

nucleus of a
guard, cell

stoma?
£ ^gtiatSlcell

A surface view and cross section of the
specialized epidermal cells which make a
passageway, to the air spaces within the leaf.

STRUCTURE OF HIGHER PLANTS

The fibrovascular bundles are made up of different types of woody cells, some pitted, others
ribbed and still others strengthened by spiral or circular thickenings on the walls.

and pitted ducts until it reaches the chorophyll-bearing or green
cells, particularly those in the middle part of the leaf. The green
cells absorb the water from the tracheids. Here, again, absorp-
tion is a cell function. Oxygen for respiration and carbon diox-
ide for photosynthesis diffuse through the stomata in the lower
epidermis of the leaves, through the air spaces in the middle layer

of the leaf, and, by means of
osmosis, pass into the green
cells. In these green cells,
photosynthesis, fat manufac-
ture, and protein manufacture
take place. These processes
are considered leaf functions
because they take place in
the green cells of the leaves.
Again the function of the
organism is really a cell func-
tion.

When greatly magnified, a woody bundle of the Excess food passes into the

corn stem shows many of the tubes which are the . . . .

passageways for the food of the plant. Sieve tubes and IS Conveyed

SPECIALIZATION IN HIGHER PLANTS

— >-Foo3l travels

->:wctt^er gbe

" V P

down to especially adapted layers of cells in the stem or in the
cortex of the root, for storage in the form of starch granules, oil
globules, and protein crystals. Turnips, parsnips, and radishes are
used by people for food because of the extra plant food stored
in them. In the case
of the potato, the
extra food is stored in
an underground stem ;
in asparagus, sugar
cane, and rhubarb, it
is stored in stems
above the ground.
When the plant needs
food, a protease,
lipase, and amylase
secreted in the cyto-
plasm of the cells that
store food, change the
stored materials again
to a soluble form.
These dissolved foods
are then distributed
by means of the ducts.
Supporting cells are
usually found in con-
nection with the ducts
and sieve tubes.
These woody fibers
support the plant.
Those in the lower part of the plant strengthen the roots and
help to anchor the plant in the ground. The woody fibers of
the stems help hold up the leaves and enable them to get sun-
light which is necessary for photosynthesis.

There are pathways through which fluids pass up and down
in plants. Raw materials travel up the stem into the leaves.
Food manufactured in the leaves travels down to the roots.

STRUCTURE OF HIGHER PLANTS

jgUorfa Cells

ej»ia«rnus

ocir

In cross section, a certain leaf will show cells
arranged in an orderly fashion. One part of the
leaf contains many air spaces through which gases
are exchanged with the active surrounding cells.

All cells need energy to
carry on their work. Each
cell takes in oxygen, oxi-
dizes the food distributed
to it, and gives off carbon
dioxide and some water.
'These materials may be
distributed either through
the vascular system or by
passing from cell to cell.
The entire plant grows by
the growth and division
of the individual cells. Reproduction of the plant is too compli-
cated to discuss here, but it will be found later that it, too, is due
to the division of certain cells.

In this chapter, the shape of plant cells has been considered.
It is by their shape, organic nature, and arrangement that they are
fitted to perform certain functions. Each cell of higher plants
contains the structures discussed in a resting plant cell. It is by
the coordination of all these cells that the entire plant functions.

Questions

1. Make an outline of the specializations in higher plants, using the
headings (a) name of tissue, (b) function, (c) adaptation to function.

2. Name the structure in a higher plant corresponding in function
to each structure observed in a cell of Spirogyra.

Supplementary Readings

Coulter, Barnes, and Cowles, A Textbook of Botany (American Book Co.),

Vol. I.
Holman, R. M., and Robbins, W. W., A Textbook of General Botany (John

Wiley & Sons, Inc.).
Gager, C. S., General Botany (Blakiston's Son & Co.).

CHAPTER IX
HUMAN TISSUES

Bone cells build skeletons.

Skeletons of fish and frog.

How can the minute structure of the body be investigated? How is
division of labor performed by the human body t What are bone and
cartilage f How are the cells in a multicellular organism held together f

If a thin slice of any portion of the human body is examined
microscopically, it will be found to consist of a mosaic of minute
units called cells. It will be further found that no cell conforms to
the diagram of the typical cell. There are masses of similar cells
that build tissues, and these tissues build more complex structures
called organs. Each organ has a special duty or function. In
the human body there is greater specialization than in the higher
plant. Each tissue or group of cells is adapted to perform a par-
ticular physiological function. At the same time, all the functions
necessary for life are carried on within each cell.

The cell the unit of structure. Any function of an organism
must be considered in relation to the function of tissues or of cells,
because it is the individual cell that does the work. Fundamen-
tally, each cell possesses the complete apparatus for life. Tissues
can be compared to collections of single-celled organisms in that
they perform most of the functions that the one-celled animals
carry on ; but each group of tissue cells is fitted by shape, structure,
location, or chemical powers to perform special functions necessary
to the life of the complete organism of which it is a part. There-

WH. FITZ. AD. BIO. — 6 73

HUMAN TISSUES

Scdcnnotnaer cells of 'Sfclvox, ot t
Skin cells colonial protoyxm

cells from. «

In most organisms, cells are not separate and distinct
units, but are joined to one another by delicate strands of
cytoplasm.

fore, it may be said that all of the tissue cells work together to
accomplish the life processes of the organism. This is brought

about by differentia-
tion of structure for
division of labor.

The cells of multi-
cellular animals and
plants are not isolated
individuals, but are
probably held together
by some kind of cyto-
plasmic continuity.
Biologists have found in certain cases, and have reason to believe
that in most cases, slender cytoplasmic bridges connect the various
cells. This gives direct continuity to the cytoplasm throughout
the entire organism, and probably enables the
organism to act as a unit even though it is
composed of millions of different cells.

Many cells of the body deposit intercellular
materials, which give additional structural
strength. The amount of the deposit varies.
Bone cells deposit a large amount of such
material; epithelium produces a very small
amount. Protoplasm is the foundation sub-
stance of cells. Groups of similar cells with
their intercellular materials make up tissues.
When tissues are grouped to make a larger
structure to perform a certain function, that
structure is called an organ. Thus, the en-
tire plant or animal organism is a combi-
nation of organs built of tissues, which in turn are built of cells.
The tissues of the human body may be classified into epithelial,
supporting or connective, muscular, blood, and nervous.

Organism,

=81-311 311

OTgocrts

TiSSuces

+
Cells

The cell is the unit of
structure and function in
every organism.

EPITHELIAL TISSUE

■»*■■ *^ riill

Squamous

Problem. Study of certain epithelial cells.

Take a toothpick and gently rub the inside of the cheek and gums. Mount
the material from the toothpick in water and add just enough fountain penink
to give a slightly-bluish tint to the water. Study with the low and high mag-
nification.

I. Describe the shape, color, relative size, and structure of the cells.

II. Draw a group of epithelial cells at least five times larger than they
appear.

III. Write a brief description of epithelial cells.

Epithelial tissue. Epithelial
cells cover and line the organs
of the body. They make very
little intercellular material. Their
function is protection and secre-
tion. They may protect certain
organs against invasion of foreign
material, or, by means of their
moist secretion, guard other or-
gans against friction. The epi-
thelial cells that line the nose,
throat, digestive system, and air
tubes or respiratory system make
up the tissue called mucous mem-
brane. (A membrane is a very
thin structure consisting of a
single layer or a few layers of
cells.) The cells lining the wind-
pipe have tiny projections of
protoplasm called cilia. Germs

i '(gyp

^Lj

Jv<*

Cubicocl Columtvocr

StrcctifieSt OiliocteSL

Epithelial cells vary in shape. They may
appear as a single layer or groups of layers
of flattened, cubelike, or columnar units.

The cheeks are lined with squamous epi-

are pushed Or moved back into - thelialcells; the respiratory tract with cili-
r # ated, epithelial cells.

the throat by means of this brush-
like arrangement. They work very much like the cilia of the
Paramecium. Because of the mucous epithelium in the alimentary
canal, food slips easily through the tube with no friction. In addi-

m> SUE MM MM SCHOIIU

HUMAN TISSUES

TL" "

,*> .

secreting ceBs a simple a tubular
2globletrc*Hs multi^kdccr gWa

On olv«olai^

ana.

•»'

a compounds,
alveolar* glajioL

or cxswvpoxcrCcl ~
jpubvxlccr g'lotnol

tion to mucous cells, there are other epithelial cells in the alimen-
tary canal adapted for secreting digestive juices.

The epithelial cells lining the closed cavities of the body com-
pose structures called serous membranes. The serous membranes
line blood vessels, cover the lungs, line the chest, cover the
heart, cover the abdominal organs and line the abdomen. The

serous membranes that
cover the lungs are the
pleurae (pleura — rib) .
In breathing, when the
lungs become inflated or
larger, and compressed or
smaller, there would be
friction between the lung
and the wall of the chest,
were it not for this moist
epithelial tissue. If the
pleurae become inflamed,
the person is said to have
pleurisy. If the secretion
of fluid is interfered with, there is friction between the lungs and
the. walls of the chest and breathing becomes painful.

The covering of the heart is the pericardium (peri — around ;
cardium — heart). This membrane prevents friction between the
heart and lungs and other organs. The membrane lining the
abdomen is the peritoneum. Infection or inflammation of the
peritoneum is known as peritonitis. This condition is sometimes
brought about when an infection extends from a ruptured appen-
dix and attacks a part of the peritoneum. Friction among the
abdominal organs such as stomach, liver, and intestines is avoided
by the moist epithelial peritoneum. The abdominal organs do
not float in the abdominal cavity. If they did, jumping or bend-
ing might throw them out of place. They completely fill the

Epithelial cells may manufacture secretions. Certain
cells, globlet cells, are found in the gullet. They give
out mucin. Groups of epithelial cells often form simple
or compound glands which give off certain secretions.

SUPPORTING TISSUES 77

abdominal cavity, and are attached to each other and to the
walls of the cavity by means of the peritoneum. A portion of
the peritoneum, called the mesentery, holds the intestines to the
backbone. If any organ of the abdomen is removed a part of
the peritoneum must be cut to separate that organ from other
organs.

The outside of the body may be compared with a body cavity
in that it is covered with epithelial tissue called skin. The outer
layers of the tissue become flat and horny, and the outermost
ones are dead. The hair and nails develop from certain skin
cells.

Supporting tissues. These tissues are all alike in that they con-
nect and support the other tissues of the body. They, in con-
trast with the epithelial tissues, are noted for the abundance of
intercellular material. The main supporting tissues are bone,
cartilage, white fibrous, yellow elastic, and fat or adipose tissue.

Problem. Study of cross structure of bone.
Obtain some rib bones of a lamb from the butcher.

I. Let some of the rib bones stand in a ten-per cent solution of hydrochloric
acid for at least two weeks.

A. How does this treated bone differ from ordinary bone in appearance
and texture ? The acid dissolves out the intercellular deposits of mineral
matter, leaving only the organic material.

B. State the importance of mineral matter in the bone.

II. Burn some rib bones in a very hot flame.

A. How does the burned bone differ from ordinary bone? Since or-
ganic material fyurns, the bone cells were destroyed, leaving only the
intercellular mineral matter. Bone consists of a combination of bone
cells and intercellular material. This intercellular material is deposited
by the bone cells. It is mineral matter, largely calcium phosphate and
carbonate.

B. State the importance of the cells in the bone.

Secure some shank bones or other long bones from the butcher. Have him
saw one lengthwise so that the interior of the long bone, including the enlarged
head, may be studied.

78 HUMAN TISSUES

I. Describe the material covering the enlarged head of the bone.

A. Is this material (cartilage or gristle) shiny or dull; moist or dry;
smooth or rough ; tough or soft ?

II. How does the texture of the bone under the cartilage differ from the
bone of the shank?

III. Describe the material filling the space in the center of the bone. This
is bone marrow and consists largely of fat cells. Compare the marrow in the
head of the bone with that in the other parts.

IV. The outer membranous covering of bone is the periosteum (peri —
around; osteon — bone).

Problem. Study of microscopic structure of bone.

I. Mount a prepared slide of bone cells under the microscope. Note the
spiderlike, irregular cells arranged around a central space. In living bone, this
space is filled with blood vessels and nerves. Food passes through the blood
vessels to the cells, and wastes from the cells are diffused into the blood
vessels. The bone cells take calcium salts from the blood and deposit these
minerals around their irregular projections.

A. Explain why bone cells with irregular projections of cytoplasm
deposit greater amounts of intercellular mineral matter than they would
if these cells were perfectly round.

B. Suggest a material that probably fills the spaces among the bone
cells.

C. Draw a single bone cell five times larger than it appears under the
microscope.

D. Draw a group of bone cells showing how they fit together and
how they are arranged around the space through which the blood vessels
run. Label cell, intercellular material, and canal.

II. Mount a prepared slide of hyaline cartilage under the microscope.

A. Describe the shape of the cells.

B. Describe the formation of the cells.

C. What evidence of intercellular material is there ? The intercellular
material of hyaline cartilage appears homogeneous throughout.

D. Draw a group of cartilage cells. Label cell, intercellular material,
or matrix.

Cartilage and bone are closely related in their development,
location, and function. In the embryo, the bones are first pre-

SUPPORTING TISSUES

ceded by qartilage. In infancy, the
bones of the skull are soft and flex-
ible, because they are largely carti-
lage. One can observe the soft
texture of certain parts of an in-
fant's skull until the child is about
eighteen months old. As growth
takes place, this cartilage becomes
hard and rigid by the deposit of
mineral matter. This compact sub-
stance is then called bone. A child's
back should be carefully supported be-
cause its backbone is largely cartilage
and is, therefore, very elastic, and
may bend so much that the organs of

wy©

^cartuatfe

Magnified cross section of bone showing the arrange-
ment of cells and canals through which blood vessels
run. The outer covering, periosteum, and the center
filled with marrow can be seen in the lower diagram.

Certain cells, cartilage cells, occur
in pairs. They deposit a thick, tough
extracellular material called a matrix.

the body will be injured.
When a bone is broken,
the new part first de-
velops as cartilage and
is replaced, afterward, by
true bone. The type of
cartilage studied in the
laboratory exercise is
hyaline cartilage. It is
found chiefly on the ends
of bone. This is not the
only kind of cartilage
found in the body.
There are other types
with different functions.
One function of cartilage
is to give ease to the
motion of joints, and by
means of its tough elas-

80 HUMAN TISSUES

ticity build those parts of the body, such as the ear and voice box,
that require strength combined with some elasticity. The inter-
cellular substance of cartilage is a secretion of the cells.

flEffiU?*i£5SV Tlie I>roper s rowtn of

■3P^«3iP^ ji f^S^ bone depends upon suffi-

^S^N^^M J^$ dent Hine SaltS in the f °° d

and the presence of certain

jbone ceU valuable growth promoters

iDone, . found in food, called vita-

canal mins, which stimulate the

proper use of the lime salts

:gular projections of protcw V the bone Cells « If bone
plasm deposit calcium compounds which they obtain foes not develop properly,
from blood. An individual bone cell is also shown. irtr.tr j ■>

skeletal deformities, like
bowlegs, may occur. This will later be discussed in connection
with vitamins.

Problem. Study of other supporting tissues.

I. Place a prepared slide of fibrous tissue under the microscope.

A. Note the large deposits of wavy white fibers with cells scattered
among them. The white fibers are the intercellular material which was
secreted by the cells.

B. Draw a few cells with the surrounding fibers enlarged five times.
Label the cells and intercellular fibers.

II. Place a prepared slide of fat or adipose tissue under the microscope. The
large space filling the center of each cell is a vacuole filled with stored oil.
The cytoplasm lies just within the wall, crowded there by the enlarged vacu-
ole. The nucleus can be noticed within the cytoplasm.

A. Describe the adaptation of adipose cells for fat storage.

B. Draw a group of adipose cells. Label cell membrane, nucleus, cyto-
plasm, and vacuole.

Fibrous, elastic, and adipose tissues. The white fibrous tissue is
made strong and flexible by the intercellular fibers which are prob-
ably secreted by the cells. It builds ligaments , strong flexible bands,

FIBROUS, ELASTIC, AND ADIPOSE TISSUES

Compare this photomicrograph of a cross section
of bone with the diagram shown on page 79.

that hold the bones together at the joints. The tendons are also

made of it. These attach muscles to the bones and are commonly

called cords. In bending the

wrist or stretching the neck,

these cords are easily seen.

When elastic fibers predom-
inate in connective tissue, it

gives a yellowish color to the

tissue and is known as elastic

tissue. It is more elastic than

fibrous tissue but not so

strong. It is found between

adjacent vertebrae, insuring

elasticity to the vertebral

column. It is also found in

the walls of blood vessels.

The adipose cells store excess supplies of fat. These cells com-
pose, to a large extent, the yellow marrow of bone. Deposits

of fatty cells are in the
deeper layers of the skin
and encase organs such as
the kidneys and heart.
When the fat is needed
by the body for metabo-
lism, certain enzymes in
the cell enter the vacuole
and digest the fat.

In general, the cells of
connective tissue support
the organs and make the

Droplets of oil enter certain cells. This oil in- °

creases in volume by additional particles entering framework of the body,
the cells and crowding the protoplasmic contents of

the cell into a small mass. The cell becomes dis- The tOUghneSS of tendons,

torted. The oil may be transformed to fat. Masses of . mi p

these cells build the fat or adipose tissue of the body, the extensile Character 01

cell
irzembran^.

f^-M.

oytopl
nxxcletjt

connective tisdtte

HUMAN TISSUES

elastic tissue and cartilage, and
the hardness of bone are all due
to the composition and distribu-
tion of the intercellular material
of the connective tissue cells.

Questions

1. What is meant by secretion?

A. Name four materials mentioned
in this chapter secreted by cells.

B. Give the purpose of each material.
Name three types of epithelial tissue. Tell the function of each.
What does the burning of bone show you ?

What effect do some acids have on a bone ?

Why should the food of an infant contain mineral matters ?

Arrange in tabular form the names of the tissue cells discussed,

Certain connective tissue cells deposit
long strands of extracellular material in the
form of either yellow or white fibers.

the function of each, and an adaptation for each function.

CHAPTER X

HUMAN TISSUES

(Continued)

Babe Ruth, home run king.

Helen Wills, queen of tennis.

Why is the body able to move? What tissue in the body makes
movement 'possible? How are messages carried from one part of the
body to another? In what way are the different tissues structurally
related? What brings about coordination among the different parts
of the body? Why may blood be considered a tissue?

Muscular tissues. All movement in the human body is brought
about by muscular or contractile tissues. Whether it is the raising
of an arm, the swallowing of food, the beating of the heart, con-
traction of the pupils of the eye in response to light, or the forma-
tion of so-called goose flesh in the skin when the body is cold,
the movement is the result of changes in the muscular tissue.

Problem. Gross structure of skeletal muscle (unmagnified) .

Secure some fore shank of meat from the butcher. • Be sure to obtain a
piece that shows the attachment of some of the meat to the bone. Have the
butcher cut it up into enough sections to supply the class.

The meaty part of the shank is composed largely of a type of muscle called
skeletal muscle because it moves the bones of the skeleton. This muscle is also
called voluntary because it is under the control of the will.

I. Observe and describe the appearance of the muscle that is attached
to the bone. The contracting or shortening of this type of muscle will move the
bone by means of the strong inelastic tendons which are fastened to the bone.

II. Find a piece of beef showing the outside of the muscle. Describe the
appearance of the covering or sheath. It is made of connective tissue.

HUMAN TISSUES

connective
tissue

muscle
foersr

III. Tear or separate the muscle into parts. Notice that the muscle is
divided into little bundles. Try to remove one of the little bundles from the
others. Name and describe the tissue that separates one bundle from another.

Describe the shape of each little
bundle. Describe the arrangement
of the bundles in making up the en-
tire muscle.

Problem. The structure of skel-
etal muscle.

_ Select a tiny muscle bundle ; place
it flat on the glass slide and add a
drop of dilute iodine. Cover with a
cover glass and focus under low
power, then high power.

I. Observe the long individual
muscle fibers and find the tiny cross
markings called striations. Skeletal
muscle is often called striated muscle
because of the presence of these char-
acteristic cross markings.

II. Draw two or three muscle
fibers five times larger than they
appear under the microscope. Label
fiber and striations.

III. Examine a prepared slide of
striated muscle. Describe the ap-
pearance and location of the nuclei
scattered along each fiber.

on.

A muscle is made of bundles of muscle
fibers, each bundle surrounded by connective
tissue. A thick external layer of this connec-
tive tissue is continuous with the tendon which
is composed entirely of connective tissue.
The tendon joins the muscle to a bone.

Problem. The structure of smooth or involuntary muscle.
Mount a prepared slide of smooth muscle under the microscope.

I. How does smooth muscle differ from striated muscle in appearance and
shape of fiber and in nuclei ?

II. Smooth muscle is called smooth or unstriated muscle because of the
absence of cross-striations. It is also called involuntary because it is not under
the control of the will. It is found in many internal organs such as the walls
of the stomach and intestine, and is responsible for movement in these organs.

III. Draw and label two or three smooth muscle cells.

MUSCLE TISSUE

Muscle tissue. It is impossible to discuss muscles without
bringing in a discussion of other tissues. When a large muscle is
dissected there is found not only the basic muscle cells, but several
other related tissues. The muscle is completely covered by a
sheath of connective tissue which extends in through the muscle,
dividing it into large bundles, then smaller and smaller ones, until
the bundles, or fasciculi, are so tiny that they are almost micro-
scopical. This connective tissue furnishes support for the blood
vessels and nerves which run through the muscles. Deposits of
fat cells may sometimes be found within the muscular tissue.

Three kinds of muscles may be identified : cross-striated or skele-
tal, unstriated or smooth, and a specialized type which forms the
substances of the heart, called cardiac muscle. The units in stri-
ated muscle are probably the fibers. They have many nuclei in
contrast to the single nucleus in the elongated spindle-shaped
cells of the smooth muscle fibers. Skeletal muscle is voluntary
muscle. It is under the control of the will. Smooth muscle and
cardiac muscle are involuntary or independent of the will. Car-
diac muscle resembles vol-
untary muscle in having
cross striations.

The special function of
all muscles is the produc-
tion of motion or the ex-
ertion of physical force.
This is brought about by
the shortening or contrac-
tion of the muscles which
have the ability of return-
ing to normal condition.
These changes are known
as contraction and relaxation. Normal muscle cells are always
in a slight state of contraction known as muscular tone. This

stncctea

carcLiac smooth

There ar» three types of muscle cells. Those having
many nuclei and cross markings are called striated cells.
The spindle-shaped ones with a single nucleus aie
smooth muscle cells. An intermediate form, cross-
striated with a single nucleus, is found in the cardiac
muscle cells. Compare the three types.

HUMAN TISSUES

.triceps

Muscles work in pairs. Motion is caused by the pull
resulting from muscular contraction. If the biceps con-
tracts, the triceps relaxes; the forearm is thus pulled up.

keeps the muscles in a condition ready for work. Muscles always
exert a pull, not a push. Skeletal muscles usually occur in pairs,
one of which opposes the other. For example, in front of the

upper arm there is a
muscle called the flexor
and on the opposite
side, the antagonizing
muscle called the ex-
tensor. The former
causes the forearm to
bend and the latter
causes it to extend.

Nerve tissue. The
organs of the body are
composed of various tissues. These tissues and organs are inter-
related and brought into communication by means of the nerve
tissue. As telephone wires bring various homes of a community
into communication, so nerve tissue brings the various organs
into coordination. For example, we see a coin on the floor and
pick it up. The eyes in seeing, the mind in deciding, the body
in bending, and the fingers in picking up, all work in proper
sequence due to regulation by the nerves. The muscles actu-
ally do the work but the nerves control
the muscles. Muscles are kept in proper
tone by repeated stimulation from the nerve
cells.

If a nerve cell is examined microscopi-
cally, the cell body, cyton, with branching
projections of protoplasm and with one long
process is easily seen. The branching pro-
jections are the dendrites and the one long

A nerve is a bundle of

process is the axon. The nucleus lies near axons. Each bundle is sur-

, . ., ., , , „ - rounded by a fatty protec-

the center or the cell body. By means of tive sheath.

BLOOD TISSUE

ton

9.en3.rite£

Shecrtlx

the dendrites, nerve cells connect with each other. The axon
is the process which connects the nerve cell with a structure
remote from the cell body.

If one hears a sound and walks toward
it, an axon has carried the sound from
the ear to a nerve cell in the brain. By
means of dendrites, a connection was set
up with another nerve cell which in turn
carried the message to muscle cells. The
muscle cells contracted so as to make
walking possible. Axons vary in length :
some are microscopic while others may be
as long as two or three feet. The cell
body is always of microscopic dimensions.
Nerve cells attain the highest development
of irritability. They are the highly sensi-
tive cells of the body. They receive mes-
sages, transmit them, and regulate the
responses to these messages. Nerve tissue
will be studied in greater detail in a later
chapter.

Blood tissue. Blood is so highly fluid
that it is not usually considered a tissue. A tissue has been
defined as a group of similar cells, and blood, consequently, may
be considered a tissue since it consists of groups of similar cells.

Problem. Study of blood tissue.

Press the finger near the tip until blood congests. Prick the end of the finger
with a needle that has been passed through a flame to sterilize it. Touch a
cover glass to the drop of blood on the finger ; invert the cover slip on a glass
slide. Mount under the low, then under the high power of the microscope.

I. Describe the shape, size, and color of the more numerous cells seen.
These are the red corpuscles.

II. Examine all the substance under the microscope carefully and find
an occasional irregularly shaped cell. This is a white or amoeboid corpuscle.

terminal branches.

The unit of nerve structure
is called a neuron. This cell
has several processes, one
sometimes very long, the axon.
Although the cell body, cyton,
is microscopic, the axon, also
microscopic in diameter, may
be two or three feet long.

HUMAN TISSUES

Blood corpuscles. The red corpuscles are circular, biconcave
disks lacking nuclei. There are* approximately five million in a
cubic millimeter of normal human blood. They have a yellowish
red tinge when viewed singly, but in great numbers appear red.
This color is due to an iron-bearing compound, haemoglobin,
which is in the cytoplasm. This haemoglobin readily unites
with oxygen and just as readily gives it up when oxygen is scarce.
The red corpuscles, in spite of their extremely minute size, can
carry large quantities of oxygen. Human tissue cells are not in
direct contact with the oxygen of the air. Therefore, they de-
pend upon the specialized red corpuscles for their supply of oxygen.
The white corpuscles are irregular masses of cytoplasm con-
taining one nucleus or several nuclei. Normally, they number
between eight thousand and nine thousand to a cubic millimeter.
They move and feed in a manner similar to that of amoebas.
They send out projections' of protoplasm which engulf and digest

foreign materials. They are
sometimes called the scaven-
gers of the body because they
rid the body of germs and
other foreign material. Un-
like other body cells, they
have the power of independent
motion and can move in a di-
rection opposite to the blood
current. They can even make
their way out of blood vessels
and get into the surrounding
tissues to destroy germs.

Specialization of human
tissues. It is evident from
the preceding chapters that the different tissues of the body are
adapted to perform particular functions. Epithelial tissue is

Part of a drop of blood that has been magnified
2500 diameters and then enlarged. The cell
shown in the center with a large nucleus is a
polynuclear white corpuscle.

SPECIALIZATION OF HUMAN TISSUES

Compare this magnified drop of frog's blood
with the human blood. This is not enlarged as
many diameters as the preceding photograph.
Notice the oval shape of the red corpuscles and
the nucleus in each one.

highly specialized for secretion, absorption, and protection;
muscle tissue, for contraction; connective tissue, for binding
together various parts of
the body and for support;
nerve tissue, for transmitting
stimuli ; and blood tissue, for
circulating materials . In gen-
eral, the cells of all tissues
can perform all the cell func-
tions that are necessary for
the life of the cell. When
cells are highly specialized
and are not in direct con-
tact with the outside world,
some of their functions be-
come reduced and are practi-
cally lost. Then these cells
become dependent upon each other to such an extent that life
is impossible without this interdependence.

The tissue cells of higher animals do not have to seek food.
They are supplied with food by the blood. Certain cells store
small quantities of animal starch or glycogen and oil. These par-
ticles may be digested by the cells when the need arises. Assimi-
lation and growth remain as functions of all cells. Cells obtain
oxygen from the blood, oxidize the food for the release of energy,
and use this energy for their work. The muscle cells and white
corpuscles release energy, in the form of mechanical energy, par-
ticularly for motion. The epithelial cells use chemical energy, and
nerve cells use nervous energy. The connective tissues and red
corpuscles need only sufficient energy to perform their general cell
functions. Most of the tissue cells lose their power to divide mi-
totically. The epithelial cells and the white corpuscles are the
only ones, thus far studied, which retain this power throughout life.

WH. FITZ. AD. BIO. — 7

90 HUMAN TISSUES

Questions and Suggestions

1. Name all the tissues of the hand and give the function of each.

2. Compare muscle, nerve, and blood tissues in function and in
adaptations of their structure for the function mentioned.

3. Compare a Paramecium and a tissue cell with respect to functions
and adaptations for function.

4. Compare a Spirogyra cell and a tissue cell as to functions and
adaptations for function.

Supplementary Readings

Kimber and Gray, Textbook of Anatomy and Physiology (The Macmillan Co.).
Stohr, Textbook of Histology (P. Blakiston's Son & Co.).
Williams, Jesse F., Healthful Living (The Macmillan Co.).

CHAPTER XI
FOOD NUTRIENTS

When broken into elements

man is worth eighty-two cents.

What is a food? What is the relation of a nutrient to a food?
What is meant by dietary requirements and dietary deficiencies f

Since the cell is the basis of our make-up, and since these cells
live, grow, and work, each must have food and oxygen to carry
on the various life processes. The cells of the brain must have
food and fuel to do the part each does in the thinking process.
Muscle cells in the thumb and fingers must be nourished and given
oxygen if they are to do their work.

What is a food ? A beefsteak includes lean meat, fat, and bone.
Only a part of this can be used by the body. This part is nu-
tritious. Potatoes contain about 70 per cent of water and vary-
ing amounts of starch, protein, and mineral salts. As a matter
of fact, they contain only about 25 per cent of nutritive material.
The small per cent of cellulose which makes up the cell walls has
no more real food value than the wood of a lead pencil. It passes
through the food tube, unaffected chemically. Such parts of the
potato are called waste. Thus we see that every food may contain
both nutrients and wastes. Certain of the waste materials that
pass through the food tract undigested, serve the real and de-
sirable purpose of giving bulk to the diet.

What is a nutrient ? Any substance, such as carbohydrate, pro-
tein, or fat, that yields material for growth and repair of tissues or,

FOOD NUTRIENTS

when oxidized, can be used as fuel for the release of energy, is a
nutrient. The term nutrient is frequently used to denote the

Malnutrition exists among plants as well as animals. Many different minerals are essen-
tial for the best growth and development of plants. When soil is properly fertilized, it con-
tains all the essential mineral matters. Note the relation of minerals to plant growth.

whole food, but foods are really made of combinations of nutri-
ents. The energy which was originally stored in the food by the
plant during the process of photosynthesis, is released from the
food during the oxidation process in the body. This stored
energy is set free from the food in some active form ; such as,
muscular energy, chemical energy, heat energy, or nervous energy.
When sugars and fats are burned, either over a fire or in the body,
waste products, carbon dioxide and water, are formed ; when pro-
tein is burned in the body, nitrogenous wastes, containing some
urea and uric acid, are formed in addition to carbon dioxide and
water. All foods do not yield the same amounts of energy. The
oxidation of those foods in which sugars and fats are concentrated
in the greatest amounts, yields the most energy with the least
amount of waste. The best fuel nutrients are sugars and fats,
and the growth or building nutrients are proteins, salts, and water.
When the diet contains an insufficient amount of sugars and
fats, some of the proteins may be oxidized for the release of energy.
But proteins give off great amount of wastes which the body
usually has difficulty in disposing of effectively.

COMPLETE AND INSUFFICIENT DIETS

The energy in food is measured in terms of heat units called
calories. A calorie represents the amount of heat required to
raise the temperature of one gram of water one degree centigrade.
When we deal with food values, we use the large calorie, which
is 1000 times the small calorie. In other words, the large calorie
is the amount of heat required to raise one kilogram (1000 grams)
one degree centigrade. When we speak of the caloric value of a
food we mean the power of food to yield heat units. Food chem-
ists group our food nutrients into the five classes which were
studied in general science or elementary biology. The table on
page 94 will help you recall certain facts concerning these classes
of nutrients.

Complete and insufficient diets. Even if a person ate some
of- all the nutrients, it would not necessarily mean that he was
getting a sufficient or a complete diet. If the diet is composed
entirely of the nutrients from the same food, it is usually insuf-
ficient, and the person using this diet may suffer from malnutri-
tion. Careful investigations have disclosed that 15 to 25 per cent of
the children in the United States are suffering from malnutrition.

Gliaden and milk diet

Gliaden diet

Rats need a variety of food materials. These four-month-old rats are from the same litter
and have been fed the same quantity of food, but of different variety. Note the differences
in size.

Protein insufficiency. An investigation was made, by McCollum
and others, in a certain institution for children to discover the

TABLE OF POOD NUTRIENTS

as a
K o

fig

Xantho-proteic test ;
add nitric acid, heat,
then cool and add am-
monia — orange-yellow
is positive reaction.

. w

03
2

A. Iodine-positive reac-
tion is blue.

B. When heated to boil-
ing with Fehling's solu-
tion, the positive reaction
is a brick-red color.

Burn the substance —
if an ash is left, mineral
matter was present.

Heat the substance —
if vapor comes off, the
substance contains water.

G*
.O

■c

G
<

a
o
ffl
o

H
to

£3

Builds new tissue and repairs
cells of the body; can supply
energy.

G
o3

s .

. °3
2^

Furnishes energy for the
body in the form of heat
and work. Transformed into
fat.

Helps to build bone, and other
tissues, and aids coagulation of
the blood. Essential constitu-
ent of protoplasm.

Used as vehicle to carry
nutrients; is a solvent. It is
a regulator of the temperature
of the body and enters into,
making of all cells.

'"&

>>
©

•2
"©
ca

H
£

A. White of egg

B. Rye, wheat

C. Milk

D. Wheat

E. Lean of meat

F. Corn

Fat of meat ; but-
ter, olive oil, oil in
corn and wheat

13 •
C3 ©

8 "8

2 2
« ©

§)
O
>

=1
e3

^©

O
.3

G
'03

03
©

1— 1

w
M

Carbon, hy-
drogen, nitro-
gen, sulphur,
oxygen, phos-
phorus

Carbon, hy-
drogen, oxy-
gen

Carbon, hy-
drogen, oxy-
gen (hydro-
gen and oxy-
gen always in
the same pro-
portion as in
water, H2O)

Sodium, phos-
phorus, • sul-
phur, calcium,
and others

T3
G
03

a g

I. Protein

A. Albumen

B. Gliaden

C. Casein

D. Glutenin

E. Myosin

F. Zein

m
"8

G
o3

r 03

III. Carbohydrates

A. Starch

B. Sugar

Glucose

Maltose

Sucrose

Dextrose

Lactose

Fructose

a
1

5>'

MINERAL INSUFFICIENCY 95

cause of so many cases of malnutrition. The institution was in
excellent condition as far as ventilation, sanitary facilities, sun
porches, playgrounds, and careful supervision were concerned,
but severe malnutrition existed among the children. A careful
study of the food of the children showed that there were suffi-
cient nutrients in the foods given in the diet, but that the pro-
teins were supplied chiefly by lean meat. The children were
then divided into two groups. In one group, a quart of milk
was added to the daily diet of each child. In the other group, the
children continued on the original diet without the milk. Within
a short time there was a marked increase in body weight among
the children in the milk-fed group. The increased weight was
maintained, and there was a noticeable change in behavior. The
milk-fed group became much more active than the group of
children not receiving milk. From this and similar experiments
it was concluded that a diet composed largely of cereals, vegeta-
bles, meat, and bread does not prove satisfactory for the physical
development of the young children and that the addition of milk
furnishes the supplementary food for the type of diet that is lack-
ing in sufficiently varied animal proteins. It has also been found
that the proteins in peas, beans, and other vegetables are of less
anabolic (pertaining to the building of protoplasm) value than
those in milk, egg, and meat.

Mineral insufficiency. There seems to be a marked tendency in
the average American, to-day, to have proportionately too little
calcium in his diet in relation to the amount of phosphorus. It
may be partly in consequence of this, that millions of the school
children of the United States have been found to have defective
teeth. The calcium must not only be present in the diet, but
must be in such a form that the body is able to use it. The
utilization of calcium will be more fully discussed in a later
chapter. The list on the following page gives some of the com-
mon foods that contain various minerals.

FOOD NUTRIENTS

Sodium — common salt.

Potassium — meat and vegetables.

Magnesium — meat and vegetables.

Calcium — milk and leafy vegetables.

Sulphur — meat and vegetables. '

Phosphorus — cheese, cod, haddock, celery, spinach, and lettuce.

Iron — meat, milk, eggs, whole wheat, spinach, and

beans.
Iodine — milk, leafy vegetables, fruits, and water.

If the diet is widely varied to include a great many different
foods, sufficient minerals are obtained. When the diet is not prop-
erly varied, specific minerals are sometimes prescribed by doctors.
For example, limewater is put in the milk of infants, or medicines
containing iron are given children. The body utilizes to some
extent the minerals in this form. However, it is cheaper and
better to get the minerals from food. Here, they are bound
chemically with organic substances, in which form they are easily
assimilated by the body.

Vitamins. Certain of our foods are of great use to the body in
that they are health regulating. It is known that such foods

Vitamin^

prevents

v eye

diseases

VitaminB"

•prevents?
tberi-beri

• •*-*»**

Vitamin C

•prevents
.Scvrvy

Vitamm*iy

weveivts
ricKets

VITAMINS, A LONG-KNOWN NEED

VitctmitvE'

prevents
in. rat5

Vitamin. G

, or-

•prevents

contain certain sub-
stances known as
vitamins. Little is
known of the physi-
cal and chemical
properties of vita-
mins, although a
great deal of re-
search is being done
in this field of nu-
trition. The amount
of vitamins in food
has not yet been
measured in definite units, but is expressed by relative terms such
as abundant, rich, fair, poor, and deficient.

Vitamins, a long-known need. Writings of the ancient Greeks
show that scurvy, now attributed to a diet deficiency, was then
known, but not understood. The person suffering from this disease
loses weight, is anaemic, pale/and weak. During the Middle Ages,
the records of the Crusaders show that this disease occurred fre-
quently. The Crusaders attributed it to something injurious in
the diet rather than to the lack of some requirement. Indeed,
armies of nearly all countries have suffered from scurvy during
wars. It has appeared whenever extended campaigning or other
conditions have limited the opportunity to get fresh and varied
foods.

At one time it was impossible to supply sailors on long voyages
with fresh foods. Captain Cook, the English explorer and trader,
was one of the first to recognize the value of fresh food as a protec-
tion against scurvy. His extended voyage, which was begun in
1772, was much discussed because no scurvy appeared among the
This was true even though the voyage lasted over three

crew.

years and covered vast stretches of the South Pacific and South

FOOD NUTRIENTS

Atlantic Oceans. Such a conquest of the ancient scourge was un-
known up to that time. Captain Cook attributed his success to the
liberal use of such fresh fruits and vegetables as could be obtained,
and to the frequent use of sauerkraut and barley. Partly on
account of this experience and partly because of similar observa-
tions and controlled experiments, regulations for the British navy
have required, since 1795, that all ships' crews be supplied with
fruit juices (usually limes) and vegetables which were thought to
prevent scurvy. (Because English sailors eat limes for the vita-
min in lime juice they are often called " limeys.") Not only armies
and navies, but exploring expeditions, camps of lumbermen, and
other isolated communities of persons have suffered from scurvy.
Although this disease had indicated, during all centuries of re-
corded history, that some peculiar food substance was required,
recognition of the vitamin-character of the substance which
prevents scurvy came only in recent years (1919-1920).

A similar story is
found in the history
of the peculiar dis-
ease called beriberi.
This has also been
one of the ancient
scourges of certain
races. Definite rec-
ords, dating back to
an extremely remote

The diets of these two rats of the same age were alike in
every respect except in the kind of fat. The rat on the right
received butter which contains vitamin A; the rat on the left
received lard which lacks vitamin A. The stunted rat devel-
oped an eye disease.

Ill

period, appear
Chinese writings,
telling of the rav-
ages of beriberi.
Beriberi is characterized by inflammatory changes in the nerves
and it usually involves distortion and even paralysis of the limbs.
Like scurvy, this disease may prove fatal if it is not counteracted

PRESENT-DAY KNOWLEDGE OP VITAMINS 99

by appropriate foods. Beriberi occurs frequently in Asiatic coun-
tries where rice is the staple article of food. The unquestioned
prevalence of the disease among rice-eating people led to ^the
theory that a fungus or
bacterial growth in rice
might be the cause of this
disease. However, a de-
ficiency in the vitamin diet
is now generally held to be

thp pnn«5P nf tli k rh'<?Pn<?P Funk fed P 1 ^ 01155 of ihe same a S e &* same amounts

uie cdUbe ui uiib ui&ed&e. of rice# The one on the left ate whole rice The one

PrAc^nt Aav IrnnwrlAHo-A on the right was fed polished rice which lacks vita-
.rre&eiu uay Kiiuwieuge min B ^ gecond pigeon . g showing sym p toms f

Of vitamins. The experi- polyneuritis which can be cured by feeding it foods rich
" in vitamin B. Polyneuritis is also found in people.

ments performed in the

last few years have given us considerable knowledge of vita-
mins. Unless we include them in the diet, deficiency diseases
may result.

An interesting experiment was carried on to determine the diet
essential for the normal development of rats. Baby rats were fed
equal amounts of food with proper kinds and proportions of pro-
teins, carbohydrates, and mineral matters, but one group was given
fat in the form of lard and the other given butter instead of the
lard. The rats fed on lard failed to grow normally and they soon
developed sore eyes. The butter-fed rats grew into normal
healthy rats. Lard lacks the vitamin known as the fat-soluble
vitamin A. This vitamin occurs in milk, butter, cod-liver oil, egg
yolk, and in the leafy green parts of vegetables such as spinach,
lettuce, and cabbage, and in the yellow pigmented parts of plants
such as carrots and sweet potatoes. The lack of vitamin A causes
stunted growth, and a certain eye disease, xerophthalmia, which
may result, in permanent blindness. Taken in its early stages,
however, this disease can be cured by including in the diet some
foods containing vitamin A.

In another experiment, two groups of pigeons were fed, one on

100

FOOD NUTRIENTS

Two guinea pigs of the same litter were fed
standard diets. The one on the right did not
get any vitamin C. It lost weight, and devel-
oped scurvy which is a type of malnutrition.

polished rice and the other on whole grains of rice. In a short
time, the first group developed a peculiar nervous disease, polyneu-
ritis or animal beriberi. The
group fed on whole rice re-
mained healthy. Polished rice
lacks a vitamin known as vita-
min B. When the polyneuritic
sufferers were given food or
water solutions made from rice
polishings, they recovered.
Vitamin B occurs in yeast, milk, and in the hulls or outer cov-
erings of grains and fruit. In fact, this vitamin is found in so many
common foods that it is probably only an extreme diet of some
kind that will induce beriberi.

Two sets of guinea pigs were fed a diet containing evaporated
powdered milk in addition to the basal foods required. In the
case of one set, the
milk was heated for a
long period ; the other
set of pigs was fed the
unheated milk. The
first group developed
scurvy ; the second
group remained
healthy. Tests show
that vitamin C, which
is present in milk and
the lack of which
causes scurvy, is, in a
large measure, de-
stroyed by heat. Pas-
teurization of milk, therefore, may destroy this vitamin. For this
reason, babies that are fed on pasteurized milk should be given

Leg disease, a type of rickets, may be due to lack of vita-
min D. These chickens are the same age and received the
same amounts of different foods. Food containing vitamin
D or even sunlight will help to prevent and cure rickets.

TABLE OF VITAMINS

101

"A"

"B-

' D

, £,.

"F"

MEAT, FISH, ETC.
Lean muscle

"A'

"B*

"E"

"G"

VEGETABLES
Spinach

***

Lettuce

***

Pork, lean

>£**

Cabbage

*:**

***

•• fat

Potatoes, white

Chickens

Beans, kidney

Turkeys

Beans, navy

Brains

Beets

Liver

***

**5j

P..SK

f.**

***

Carrots

***

Heart

***

Onions

Kidneys

Peas, fresh

fc**

Fish

Asparagus

J***

Fish, roe

***

Parsley

fe**

Oysters

***

Parsnips
Celery

**
*

NUTS
A'monds

Cauliflower

Brazil nuts

Cucumbers

Chestnuts

Mushrooms w

Cocoanuts

Squash

5S*

Filberts

FATS AND OILS

Hickory nuts

Cod Liver Oil

***

Peanuts

Butter

***

Pecans

Corn Oil

Walnuts, English

Margarine, oleo

■• black

Mutton fat

DAIRY PRODUCTS

Beef fat
Cottonseed

Milk, whole
" skim

**
*

**
*#

*
*

**
*

***

Olive

"• condensed

FRUITS

«■ •• sweetened

Prunes

«• evaporated

Apples

" powdered

Bananas

Butter

***

Grapefruit

***

Cheese, whole milk

Lemon juice

***

MISCELLANEOUS

Pineapples

Yeast

***

Limes .

Molasses, beet

Orange juice

***

•« sorghum

Tomatoes, raw

S:**

***

•• cane

•• canned

*#*

***

Eggs

Raisins

Eggs, yolk

***

GRAINS AND SEEDS

Alfalfa

. ■•-:-

je##

Wheat, whole

?**

Clovers

***

Jt *

" germ

**#

***

Green grass

***

" bran

Timothy

***

Corn, white

***

Tea

<> yellow

Oats
Barley
Rice, bran
Cottonseed

*
*

**
**

**
*

abun
imp
nsul
defic

dant
e

ficie
ent

102

FOOD NUTRIENTS

other foods to supply this vitamin. Vitamin G occurs largely in
citrus fruits such as lemons and oranges, and in tomatoes and

Underwood & Underwood
Sunbaths are valuable for insuring the proper functioning of the body. Irra-
diation guarantees an optimum storage of calcium in the body.

cabbage. During the early days of the great World War, before
the United States had entered the fight, a foreign ship entered
Hampton Roads with hardly enough healthy sailors to man the
vessel. The ship had been transformed into a commerce raider, a
gun had been mounted both forward and aft, and the hold was filled
with enough canned and concentrated foods to provision the crew
of sailors and marines for many months. But fresh foods were
lacking and the crew was repeating the experience of many sailors ;
it was suffering from scurvy. Orange juice, tomato juice, milk,
raw cabbage, celery, carrots, and water cress, which are known to
contain vitamin C, were, at once, included in the diet of the sailors
and they soon recovered.

Many animals suffer from a disease known as rickets, which is
an improper formation of bones. This seems to be caused by the

PRESENT-DAY KNOWLEDGE OP VITAMINS

103

non-deposit of the mineral calcium which is present in certain
foods. The head of a rachitic animal usually becomes bulky, and
the bones at the knees and ankles, become enlarged. For experi-
mentation, a set of rats was fed a diet which contained vitamin A,
but lacked another substance known as vitamin D; another set
of rats was given vitamin D in the form of cod-liver oil. The first
group developedrickets ; the second group grew normally. : Many
physicians and scientists have observed and reported that the
exposure of rachitic children to the rays of the sun has brought
about an improvement and cure of rickets. In these cases there
were plenty of calcium and phosphorus already present in the
blood, and the sunlight is thought to have influenced, in some
way, the activities of certain cells so
that they could make efficient use of
these minerals. Other scientists have,
found that it is the ultra-violet rays in
sunlight, which are instrumental in
preventing and curing rickets. These
curative rays cannot pass through
ordinary window glass, but will pass
through quartz glass.

If babies are given food deficient in
vitamin D, but which has been exposed
to these light rays, the food can be
activated so as to cause it to have the
same effects as the ultra-violet rays.
Cotton-seed oil, which ordinarily con-
tains no vitamin D, becomes anti-
rachitic when exposed to sunlight.

Two scientists, Evans and Bishop,
have added another member to the
vitamin family. They found that this vitamin, which they named
vitamin E, has a marked influence upon the fertility of rats.

Sunsuits give children the benefit of
the direct rays of the sun.

104 FOOD NUTRIENTS

When a diet lacking certain food stuffs which contain vitamin E is
fed to rats, the reproductive organs of both the male and female
will be affected. Investigators have found that a deficiency of this
vitamin in the mother rat will lead to the resorption of the embryos
even after development has proceeded in a normal manner for a
week or more. Other research workers have found that this vita-
min is present in meat, wheat germ, rolled oats, yolk of egg,
milk fat, and lettuce.

In the biology of to-morrow, there will probably be other vita-
mins to add to the group already listed. There has been some
work with what has been called vitamin G or vitamin P-P (pellagra-
preventive). Lack of it is known to induce pellagra, a disease
afflicting many people in the southern states. The late Dr. Joseph
Goldberger, of the United States Public Health Service, found
that certain foods contain this pellagra-preventive, but as yet the
amount of the preventive substance in various foods has not been
conclusively determined.

Diets. Malnutrition was at one time attributed to poverty,
but scientists have found that there is almost as much malnu-
trition among the wealthy as the poor. Proper dieting is a matter
of selecting different foods that give all the elements essential to the
health of the individual. Many dietary studies have been made in
various countries and among people doing different types of work.
From these studies and from experiments, certain foods have been
recommended that are thought to make for physical fitness.

All diets should include proteins, fats, and carbohydrates, prob-
ably in the proportions of one, three, and six. They should in-
clude, among other foods, a quart of milk and some leafy or raw
vegetable so that a sufficient supply of vitamins can be guaranteed .

It should be kept in mind that people of different ages, sizes,
weights, and occupations naturally require different amounts of
calories of foods. The following table is suggested for determining
the number of calories of food needed by boys and girls :

DIETS

105

Boys

*From 12-13 2300-2700

From 13-14 2500-2900

From 14-15 2600-3100

From 15-16 2700-3300

From 16-17 2700-3400

, Girls
1850-2150
1950-2250
2050-2350
2150-2450
2250-2550

Problem. Study of personal diets.

I. Consult the age and weight tables in the Appendix and find out whether
you are normal, underweight, or overweight.

II. From the table given above, determine the number of calories you need
per day.

III. Make out the following outline and list the foods eaten by you on a
definite day.

Proteins

Fats

Carbohydrates

Breakfast
1
2
3
Luncheon
1
2
3
Dinner
1
2
3
Between meals
1
2
3
Totals

* New York Association for Improvement of the Condition of the Poor.

WH. FITZ. AD. BIO. — 8

JOG FOOD NUTRIENTS

A. Consult the tables of caloric values of foods in the index.

1. Fill in the number of calories of protein, fat, and carbohydrates for
each food you have listed. Total the columns.

2. Add the totals. Compare your actual totals with the number of
calories you really need according to the given table.

a. Are you eating enough, too little, or too much food ?

b. Is the ratio of protein, fat, and carbohydrates correct ?

c. Consult the suggestions given in the discussion of foods and see
-whether all the types of food needed are in your diet.

3. What changes, if any, should be made in your diet ?

a. Give reasons in each case. The age-weight tables are not
authentic opinions as to malnutrition. They are, however, some-
what indicative of the condition of nutrition.

Questions

1. Define a food and a nutrient.

2. What elements in foods are fuel for oxidation ?

3. What are vitamins ? What are their value in the diet?

4. What are deficiency diseases ? Name several.

Supplementary Reading

Harrow, Benjamin, Vitamins (E. P. Dutton & Co. Inc.).

McCollum & Simmonds, The Newer Knowledge of Nutrition (The Macmillan

Co.).
Sherman, Chemistry of Food and Nutrition (The Macmillan Co.).
Stieglitz, J. O., and others, Chemistry in Medicine (Chemical Foundation Inc.).

CHAPTER XII

THE TEETH
AND THEIR CARE

Continuous growth of teeth.

Fangs of snake inject venom.

What are some causes of bad teeth? What is meant by the hygiene
of the teeth f Why are the teeth of the average American probably
inferior to those of his great-grandparent f

Detailed structure of teeth. Not only are teeth important in
helping to prepare food for use in the body, but they are invaluable
in maintaining the health of the body. The teeth, embedded in
sockets in the upper and lower jawbones, are especially fitted for
the work that they have to do. Each tooth has a root which con-
sists of one or more divisions contained in the socket; a crown
which projects above the gums ; and a neck which is the narrow
portion at the edge of the gum.

Each tooth is composed principally of dentine. In the center
of the dentine is the pulp cavity which tapers into the root canal
and ends in a small opening at the extremity of the root. The
pulp cavity is filled with loose connective tissue containing blood
vessels and nerves which enter through the root canal. The
dentine is crowned with a hard layer of enamel composed mostly
of calcium. The dentine of the root is covered with cement which
has practically the same composition and structure as bone, but
is much harder. Every normal person has two sets of teeth dur-
ing his life, the first or temporary, and the permanent. There are
twenty temporary teeth, ten in each jaw : four sharp-edged in-

107

108

THE TEETH AND THEIR CARE

*\>cfc

Todt occrcH

Blood vessels and nerves
enter the tooth cavity, which
consists of connective tissue,
through the root canal. This
cavity is well protected by the
enamel, dentine, and cement.

cisors, two sharp canines, and four molars especially adapted for
crushing and grinding. The first teeth of the temporary set usu-
ally begin to appear when the child is six
months old and the last appear when he is
about two years old. The teeth of the
lower jaw usually develop before the cor-
responding ones of the upper jaw.

The permanent teeth push out the tem-
porary teeth. The milk molars are fol-
lowed by the permanent premolars, but
there are no predecessors for the perma-
nent molars.
The first permanent teeth usually appear
about the sixth year while the last ones may not appear until the
twenty-fifth year. The molars are the first to appear, then the
two central incisors about the seventh year, the two lateral in-
cisors at eight, the bicuspids at nine and ten, the canine at eleven
or twelve, the second molars at twelve or thirteen, and last are
the third molars or wisdom teeth.

The first permanent teeth to appear are the upper first molars
which do not replace any of the milk teeth, but come down behind
the second temporary molars. When the temporary teeth of chil-
dren are neglected these six-year molars are often neglected, and
consequently have to be extracted early in life.

Arrangement of teeth. When the mouth is closed the upper
front teeth protrude slightly over the lower front teeth. If the
teeth are irregular or out of position, this arrangement is changed.
Adenoids are sometimes responsible for narrowing the jaw and
throwing the teeth out of position. People with poor formations
of teeth can not chew their food properly and digestion is therefore
impaired. When teeth are crowded and out of place, the food may
remain lodged between the teeth and cause them to decay. The
normal contours of the face are changed by malformations of the

CARE OF THE TEETH

109

teeth. In order to insure good health, teeth should be straightened
and adjusted. Dentists are usually able to obtain better results
in correcting these malformations if the teeth are not fully grown.
Care of the teeth. When the teeth are not cleaned frequently,
a substance known as tartar often forms upon them, usually near
the gums, and pre-
vents the bacteria

•temporary Canine
"temporary ny

twnpownrj£ inoisors ; replaced 'by incisors

replace**.
WJ>icuspias

The teeth of a six-year-old child are temporary teeth with the
exception of the six-year molar. This is the first permanent
tooth to cut through the gum. Its position is just back of the
milk molars.

inci^org

from being rubbed
off by the action of
the tongue. For this
reason artificial
means must be em-
ployed to keep the
teeth free from this
gummy tartar
which later becomes
hard. The teeth
should be brushed
at least twice a day
with a tooth paste
or powder which
contains some sub-
stance, such as
chalk, which is hard
enough to rub off
all deposits but not
hard enough to in-
jure the enamel of
the teeth. The
teeth should be brushed with a fairly stiff brush after each meal,
in order to remove all particles of foods, and to stimulate the
circulation of blood in the gums. The mouth cavity should then
be thoroughly rinsed out with a mouth wash or a solution made

Permanent teeth are for biting, chewing, and grinding.

110

THE TEETH AND THEIR CARE

by dissolving a half teaspoonful of salt in a glass of warm water.
Fruit acids such as dilute lemon juice or vinegar should be used
occasionally. If food lodges between teeth, it should be removed
by dental floss. A metallic toothpick or pin should never be used
as it may chip or crack the enamel. Wooden toothpicks should
also be avoided as they tend to cut and irritate the gums. Silk
thread is not an adequate substitute for dental floss because it is
not sterile and it may cut the gums.

Periodical visits to the dentist. In spite of the best care, the
tartar cannot be entirely removed from the teeth with a brush.
The bacteria which are held in the soft tartar will probably
decay the food left in the teeth. Sometimes the fermenting of
sugar between the teeth and the acids formed by bacteria will
dissolve the enamel, causing soft spots or tiny cavities in the teeth.
The soft dentine is then exposed to the decay action of the bac-
teria. Once a year, at least, a visit should be made to the dentist
for the purpose of having the teeth cleaned and any small cavi-

By skillful dental attention, projecting incisors of the upper jaw can be made to
articulate, that is, meet the lower jaw.

ties detected and filled before they seriously weaken the teeth.
When accumulated tartar remains on the teeth, the gums may

RELATION OF DIETS TO TEETH

111

The contours of a profile may be changed by
straightening the teeth.. These outlines are
the profile of a boy before and after he had
received dental treatment.

recede, become swollen and inflamed, and the teeth may loosen
in their sockets. This is one type of pyorrhea which a dentist
may be able to prevent.

When the teeth decay, pus is
frequently formed and absorbed
by the blood. The pus may
travel through the body and
may settle in the valves of the
heart, causing a heart defect, or
in the joints, causing rheuma-
tism. Besides this, decayed
teeth give the breath an objec-
tionable odor and the mouth an
unsightly appearance. Physicians often insist that patients have
the teeth examined and treated before they will treat them for
other ailments. The disorder sometimes disappears when the
teeth are put in good condition. Defective teeth do not have as
great grinding power as have sound teeth, and, therefore, hinder
digestion.

Relation of diets to teeth. More important than repairing
unsound teeth is the building of sound teeth. Foods containing
calcium should be eaten so that the bone cells can deposit suffi-
cient calcium to build strong teeth. Every diet should include
some foods containing vitamin D, so that the body will be stimu-
lated to make the greatest possible use of the calcium. Foods
that demand chewing, such as breads made of whole cereals, toast,
apples, and celery, are also essential for the development of good
teeth. Hard foods cause the teeth to move slightly in their
sockets. This has a massaging effect upon the gums and tends to
promote circulation through the pulp cavity and the part of the
gum holding the teeth in the bony sockets. One of the reasons
why former generations had better teeth than many of the people
to-day, is because they ate coarser foods which supplied minerals

112 THE TEETH AND THEIR CARE

and vitamins in greater quantity than our present refined and rich
foods. The coarse foods act like tiny toothbrushes in scratching
food particles off the teeth and polishing their surfaces.

Causes of teeth decay. Other conditions besides lack of indi-
vidual care may cause defective teeth. A low resistance of the
teeth to decay is frequently caused by some defect in the devel-
opment of the individual. For example, some babies have a thin,
faulty skeletal development which naturally affects the forming
of the teeth. This may be caused by a deficient diet — both of
the expectant mother and later of the child. The calcification of
the temporary teeth and the permanent molars takes place dur-
ing the child's prenatal life and if the mother does not get the kind
of food that is essential for the development of the teeth of the
unborn child, the chances are that its teeth will be defective.
Again, if a child's diet lacks vitamin D, it is possible that the
proper amount of calcium for forming teeth will hot be deposited.
Dental attention to the first teeth is often neglected because
parents fail to realize the necessity of it or cannot afford the high
cost of such care. Frequently, the failure on the part of children
to tell their parents of cavities in their teeth, either because they
are too young or because they are afraid of being hurt by the
dentist, is the cause of poor teeth. The lack of competent dental
facilities in many communities is by no means an infrequent
reason for bad teeth.

Problem. Survey of the condition of the teeth.

Use a mirror or mirrors to assist you in your survey.

I. Note your bite by closing the teeth and drawing back the lips.

A. Describe any malformations such as teeth out of place, upper teeth
protruding over lower teeth, or lower teeth extending over upper teeth.

B. Discuss the importance of having the teeth straightened.

C. What is the advantage of having an orthodontist (a dentist special-
izing in treating irregularities of the teeth) straighten your teeth rather
than a regular family dentist ?

CAUSES OF* TEETH DECAY 113

II. By means of a small mirror, observe the front surfaces of your upper
teeth, the inner surfaces of the lower front teeth, and the inner surfaces of the
back teeth. Use the tongue to explore the surfaces of the teeth for tartar.

A. Describe the appearance and location of any tartar.

B. Discuss the origin of tartar.

III. Look carefully at the gum line of the teeth. Describe the appearance
of any tooth from which the gum has receded, exposing the neck.

A. Why will such teeth decay quickly ?

B. What effect will the removal of tartar and proper massaging of
the gums probably have on such teeth ?

IV. By comparing your teeth with the diagram on page 109, name and
describe the condition of any tooth showing a cavity. In each case describe
the apparent extent of the cavity. Explain why your examination is not as
complete as a dentist's ?

V. If you have any roots of broken teeth left in your gums, give, briefly, the
history of each. By referring to the diagram determine the name of each.

A. Discuss whether the loss of the tooth could have been prevented.

B. Discuss dangers from the presence of roots left.to decay in the mouth.

VI. If you have any spaces left by extracted teeth, what are your plans in
regard to these spaces ? Again refer to the diagram to name the missing tooth.

VII. When did you last visit a dentist ? When will you again visit one ?

VIII. If you are unable to detect any defects in your teeth, tell why you
cannot conclude that your teeth are in good condition ?

IX. By means of red and blue litmus, test whether the reaction of your
mouth is acid or alkaline. Note. When blue litmus turns pink, an acid is
present. When pink litmus turns blue, an alkali is present.

A. State one possible source of acid-formation. What effect has acids
on enamel ?

X. What advice can you give your parents in regard to the care of the
teeth of your small brothers and sisters ?

XI. Discuss the value of X-rays in dentistry.

Questions

1 . Describe the arrangement, number, and kinds of temporary teeth.

2. Describe the arrangement, number, kinds, and structure of per-
manent teeth.

3. Explain the hygienic methods of cleaning teeth.

4. What is the relation of proper diets to good teeth ?

5. What are some of the causes of bad teeth ?

CHAPTER XIII

THE
DIGESTIVE SYSTEM

crop

iyytrb

.caecum

.dooccal opening

Part of food tube of worm.

Alimentary canal of a bird.

What similarities and differences are found in the digestive sys-
tems of a frog and of a man. How is food prepared for digestion?

We shall find in dissecting a frog and studying its digestive or-
gans that its digestive processes are in many ways similar to those
of man.

Problem. Study of the internal organs of a frog.

Place the frog to be studied in a covered jar. Pour a little ether into the
jar or put in the jar a sponge saturated with ether. When the animal is
dead, remove and place it, with the ventral side up and the head away from
you, in shallow water in an individual dissection pan. • Pin the legs out so
that they will not interfere with the dissection. By means of forceps, lift up
the skin in the center of the body and cut a very small opening near the pos-
terior end. Insert the point of the scissors into the opening and carefully cut
along a median line to the mouth. Again insert the scissors near the legs and
cut through the muscles under the skin. Be sure to cut through the pectoral
girdle of bones near the forelegs. Insert the scissors at the anterior and pos-
terior ends of the median slit and cut at right angles on either side. Turn
back and cut off the loosened flaps of skin and the underlying muscles, in order
to expose the internal organs. If the specimen is a female, remove nearly all
the eggs so that the organs may be more readily seen.

I. Make an outline drawing, natural size, of the shape of the frog.

II. Observe the cone-shaped heart midway between the fore limbs. If the
heart is still beating, it does not indicate that the animal is alive. It means

114

PROBLEM 115

that all of the cells of the body are not yet dead, especially the cardiac muscle
cells. Draw in the outline, the heart in its proper position.

III. The lungs lie on either side of the heart partly covered by the liver.
By means of a blowpipe passing from the mouth to the windpipe of the frog,
gently innate the lungs.

A. Account for the color of the lungs. Press them with the wooden
end of the dissecting needle. Are they spongy or compact ?

B. What is the relation of the texture of the lungs to the amount
of air present ?

C. By means of a hand lens determine and describe the external and
internal structure of the lungs. Draw the lungs in position in your
outline.

IV. The large, lobed, reddish-brown organ that lies to the right and be-
hind the heart, and covers part of the lungs, is the liver. It is one of the diges-
tive glands. Note the greenish bile sac (or gall bladder) attached to the liver.
Sketch in your outline the liver and gall bladder.

V. On the left side of the body note the long, tubular, pouchlike stomach.
Push the handle of the dissecting needle down the gullet into the stomach.
Draw as much of the stomach as can be seen.

VI. The tubular structure leading from the stomach and filling the lower
part of the body cavity forms the intestines. At the lower end of the small
intestine the tube becomes larger and disappears between the two thighs.
This large tube is the large intestine, the last part of which is the cloaca. The
large intestine is similar to the large intestine in higher animals in that it
excretes the solid wastes of the body, but it is also a reservoir for nitrogenous
wastes and reproductive cells. In this respect it is different from a true large
intestine and consequently is called a cloaca. Draw the small intestine, lsfrge
intestine, and cloaca.

VII. In the U-shaped loop made by the stomach and the small intestine
is a small, light-colored, pear-shaped organ. This is an important digestive
gland called the pancreas. Draw the pancreas.

VIII. Describe how the internal organs of the frog are held in place. This
structure is termed the mesentery.

IX. Label heart, lungs, liver, gall bladder, stomach, small intestine, large
intestine, cloaca, and pancreas.

X. After all the required drawings are made, take your specimen from the
dissection pan and wrap it in mimeograph paper which has been moistened

116 THE DIGESTIVE SYSTEM

in a salt solution. Keep it in a cold place so that you may continue your
investigation the next day.

XI. Write a paragraph describing the internal organs of the frog, as seen
from the ventral view.

Problem. Study of the food tube or alimentary canal of the
frog.

By means of your forceps, lift up the heart and carefully cut it out of the
body. Lift up each lung, and carefully cut it out. In a similar manner re-
move the liver.

I. Describe the organ leading into the stomach. This is the gullet or
esophagus. Place the blunt end of the dissecting needle in the anterior
end of the gullet. Carefully force it through the gullet. Where does it
lead ? Is the passageway a continuous one or did the needle meet any ob-
structions ?

II. Make another outline drawing of the frog and sketch in it the alimentary
canal. Label gullet, stomach, small intestine, large intestine, and cloaca.

III. Remove the alimentary canal. The two small brownish red struc-
tures near the backbone in the center of the body cavity are the kidneys. The
kidneys remove the nitrogenous wastes (urea) from the blood. Each one is
connected to the cloaca by a small duct.

IV. Write a paragraph describing the alimentary canal.

Problem. Study of the internal organs of man.
Remove the front wall from the mannikin.

I. Contrast the chest and abdominal cavities of man with the body cavity
of the frog. Note the presence of a partition, the diaphragm.

II. Locate and describe the organs in the chest or thoracic cavity.

III. Name all the abdominal organs observed in the frog, which can be
identified in man.

IV. State four easily recognized differences in structure or position be-
tween the organs of the frog and man. The large intestine takes care of solid
wastes only ; therefore, it is a true large intestine and not a cloaca.

V. Make an outline drawing of the mannikin and sketch the organs in posi-
tion. Label chest cavity, diaphragm, abdominal cavity, heart, lungs, liver,
stomach, small intestine, and large intestine.

THE MEANING OF DIGESTION

117

Infcestin

Problem. Study of the digestive system of man.
Remove the heart and lungs from the mannikin.

I. Locate the gullet and describe its exact position, including origin and end.

II. Remove the intestines and locate the pancreas and the posterior end
of the large intestine called the rectum.

III. Describe the connection of the pancreas and liver with the small in-
testine.

IV. Compare the alimentary canal of the frog and man as to relative size
of organs and as to complexity in structure.

V. Make a diagram of the digestive system and label throat, gullet,
stomach, small intestine, large intestine, rectum, pancreas, and liver.

The meaning of digestion. Before a cell in the brain, in the
tip of the toe, or any other part of the body can use the meat
or the vegetable
that is eaten,
many changes,
physical and
chemical, must
take place in the
food. The organs
that are particu-
larly adapted for
carrying the food
particles, for pre-
paring it for ab-
sorption, and
making it ready
for use by the
various body
cells, make up
the digestive sys-
tem. In the thrashing of grain, much of the useless is sepa-
rated from the useful parts of the cereal. So, in the digestive

The digestive organs of the frog have been removed from the
body to show some of the digestive glands and the continuous ali-
mentary canal. The bladder is one of the excretory organs which
drains into the cloaca. The latter is the receptacle for materials
from the alimentary canal, reproductive organs, and the bladder.

118

THE DIGESTIVE SYSTEM

system, the part of the food that cannot be used is separated
from the nutrients. This process may be called a refining pro-
cess. The waste or indigestible
part of the food is ultimately
expelled from the body. The
nutrients are made ready for
absorption by the action of
various juices. In this diges-
tive process the nutrients are
reduced to simpler and simpler
organization or certain standard
forms to enable them to pass
through the walls of the blood
vessels. For example, the pro-
teins in eggs, milk, and meat
are reduced to standard protein
products ; the starch in bread
and potatoes and the sugar in
fruits, candies, and carrots are
all reduced to a standard car-
bohydrate product. The pro-
cess of digestion really consists
Man is a collection of tubes and cavities, of refining, digesting, and stand-

The spinal column is a bony tube, the nerve .

cord a solid rod made of delicate tissue, and the ardizing processes.

food tube a long, continuous, pipelike canal. .

Digestive organs. I he diges-
tive system may be said to consist of two groups of digestive
organs, those making up the alimentary canal or food tube in
which foods are actually digested, and the accessory organs, the
glands, which make or secrete the juices for digestion. A gland is
a collection of epithelial cells that secretes a juice. Some of the
digestive glands are large organs outside the food tube, such as
the pancreas and liver, and others are minute structures, in the
lining of the food tube, as the gastric, peptw, and intestinal glands.

nasal cavity...
mowfh Cavity-

fhomcic Cavity

dxapKrag , iT>-

abdominal

Cavity

ALIMENTARY CANAL OF MAN

119

gx\\ Naaa<p£

JDjIe^lw

When the digestive glands are located some distance from the
food tube, they have a tube or duct which effects the discharge
of the secretion into the alimentary canal.

Alimentary canal of man. The alimentary canal is a tube pass-
ing through the body, in which food is made ready for the use
of the organism. While food remains in the canal, it is actually
separated from the body because it can pass out of the body at
the posterior end of the tube without having affected the other
organs of the
body. Consider
the alimentary
canal of the
worm. It is a ,
straight tube * ive f
passing from the
anterior to the
posterior end of.
the animal's
body. It is a
tube within a
tube. Before
food is actually
in the body, it
must get from
that inner tube
into the sur-
rounding struc-
tures. The ali-
mentary canal of
man is a contin-
uous tube from
the mouth to the anus or end of the large intestine. There is much
variation in width in various sections, and it is twisted and coiled

stomach

"pcrncreccs

.transverse
coioru

GscenAing
colore-

small
intestine

vermifc
appenc

colo TV

The digestive organs of man are displaced to some extent in this
illustration, in order to show clearly their relations to each other. They
are somewhat similar to those of the frog. Note the absence of a
cloaca, however. Higher animals have a large intestine but no cloaca.

120

THE DIGESTIVE SYSTEM

to a great extent in some parts, but is just as truly a tube as
the simple straight alimentary canal in the worm's body. The
alimentary canal consists of the mouth cavity with its accessory
organs : the teeth, tongue, glands, throat or pharynx, esophagus,
stomach, the small intestine, and large intestine.

Mouth. The mouth cavity, nearly oval in shape, is lined with a
soft membrane which is kept moist by saliva secreted from glands.
The palate or roof of the mouth consists of a hard portion in front,
Wkm* ...;£ formed by a bone covered by

mucous membrane, and of a soft
portion farther back containing
no bone. The hard palate forms
the partition between the mouth
and nose ; the soft palate arches
backward, and from the middle of
its lower border there hangs a
pointed portion of the soft palate
called the uvula (little grape).

The tongue is a muscular organ,
and has on its upper surface many
small projections called papillae.
These papillae contain certain nerve cells that make it possible
for us to taste sweet, bitter, sour, and salt. When these special-
ized structures (taste-buds) are stimulated by the food, the secre-
tion of saliva is increased and gastric fluid in the stomach starts
to flow. The tongue helps mastication by pushing and rubbing
portions of the food against the roof of the mouth, and also guides
the food into position for chewing. The tongue assists in swallow-
ing by manipulating the food into small masses and pushing them
back to the throat cavity.

Due to the complex movement of the lower jaw, up and down,
forward and back, and from side to side, the teeth shave, slice,
crush, and grind the food. The broad surfaces of the molars

pcercfticl
glatvU-

SubmasciHai^
Sublingual

There are three pairs of salivary glands
which empty into the mouth. The teeth
may become coated with tartar which is par-
tially a deposit from the saliva.

SALIVA 121

help in the grinding process. During this process the food is
thoroughly mixed with secretions from the glands of the
mouth.

The chief secretion of the mouth is supplied by the salivary
glands. These are three pairs of compound saclike glands, the
parotid, sublingual, and submaxillary. A parotid gland is placed
just under and in front of each ear; the ducts from the glands
pass forward along the cheek and open opposite the second molar.
The submaxillary glands are situated below the jaw and under the
tongue, and open into the mouth cavity underneath the tongue.
Several of the small ducts from the sublingual glands also open in
the floor of the mouth beneath the tongue. The secretion of these
salivary glands, mixed with the secretion of the small glands of
the mucus epithelium, is called saliva.

Everyone has probably experienced an unusually large flow of
secretion from the salivary glands when appetizing food is seen or
smelled. The stimulation of the salivary glands may also be
brought about by the thought of food that is liked, especially
when one is hungry. This is known as psychical or mental stimu-
lation. Flavoring substances and extractives that stimulate the
taste buds furnish chemical stimuli, and the pressure of food in
the mouth and the action of irritating substances cause a mechan-
ical stimulation.

Saliva. Saliva consists of water, inorganic salts, some mucin,
and the enzyme ptyalin or salivary diastase. Saliva is usually
slightly alkaline in its reaction and has four distinct functions :
(1) it assists in mastication and swallowing by moistening and
softening the food; (2) it lubricates the food and enables it to
slide smoothly down the esophagus ; (3) it dissolves dry and solid
food such as salt and sugar, thus enabling us to taste them,
and thereby stimulating a further flow of salivary and gastric
juices; (4) the enzyme ptyalin acts upon starch, converting
it into sugars, dextrin and maltose. These are intermediate

WH. FITZ. AD. BIO. — 9

122 THE DIGESTIVE SYSTEM

products in the digestion of starch. They are simpler products
than starch, but not simple enough to be used by the body. The
change, due to ptyalin, takes place when there is a slightly alka-
line condition. Saliva that is distinctly acidulous hinders or arrests
the digestive process. Boiled starch is changed more rapidly and
completely than raw, but food is rarely retained in the mouth
long enough for the saliva to more than> begin the transformation
of starch.

Throat and esophagus. The mouth cavity narrows to form
the pharynx or throat cavity. It is shaped somewhat like a funnel,
with its narrow or constricted end turned downward to form the
beginnings of the esophagus and the windpipe. There are seven
openings in the throat cavity, leading to the nose, ears, mouth,
larynx, and gullet. Two, in front above, lead into the back of the
nose and are known as the internal nasal openings. Two, one on
either side above, lead into the ears and form the openings to the
Eustachian tubes. One midway in front connects with the mouth.
Two below, one opening into the windpipe through the glottis and
the other behind the glottis into the gullet.

The pharynx is a passageway for air from the nose to the glottis,
and for food from the mouth to the gullet. When the food is ready
to be swallowed, it is brought together on the upper surface of the
tongue and pressed backward into the pharynx. Then the muscles
in the pharynx contract, drawing the pharynx upward and caus-
ing it to dilate to receive the food. The muscles then relax, caus-
ing the pharynx to sink and forcing the food into the esophagus.
At this instant, breathing is temporarily suspended and the air
passages closed against the possible entrance of food. The soft
palate is drawn back, thus closing and protecting the nasal pas-
sages. The entrance to the windpipe is shielded by being pulled
forward under the base of the tongue. There is an additional
safeguard through the folding down of the epiglottis, a special-
ized cover. When food is once within the esophagus, breathing

THROAT AND ESOPHAGUS 123

may be resumed. Practically no digestion takes place in the
pharynx due to the facts that food is swallowed quickly and no
enzymes are secreted here.

The esophagus is a comparatively straight tube, about nine
or ten inches long. It descends in front of the spine, passing
through the diaphragm and terminating in the stomach. It has
one set of muscles extending around it circularly and another layer
of muscles longitudinally arranged. By a series of contractions of
the circular and the longitudinal muscles, food is passed by a series
of wavelike movements into the stomach. Once the top ring of
muscles is stimulated by the swallowing of the food, a wave of
contraction goes through the full length of the gullet, causing
the food to enter the stomach. This series of rhythmic, wave-
like contractions of circular and longitudinal muscle fibers which
affect successive portions of the tube downward is called peri-
stalsis. The constricted portion is always preceded by an area
of relaxation which renders the contraction more effective in
forcing the contents onward. The direction is normally the
same, and the action is under the control of the nervous system.
This movement might be compared with placing a large marble
in a narrow rubber tube and forcing it through by successively
pinching the tube.

During the processes of mastication, moistening, and swallow-
ing, the food is reduced to a soft, pulpy condition. Any starch
it may contain begins to change into sugar in the mouth, but
it remains in the mouth, throat, and esophagus so short a time
that digestion cannot be completed in them.

Questions and Suggestions

1. How does the body cavity of the frog differ from the cavities
in man's body ?

2. Name three purposes of the digestive process.

3. Compare the alimentary canals of the worm, frog, and man,
stating all similarities and differences.

124 THE DIGESTIVE SYSTEM

4. If saliva were acid in reaction instead of alkaline, what effect
would it have on the teeth ?

5. What are the functions of the soft and hard palates ?

6. State the uses of the tongue.

7. What is the importance of saliva in digestion ?

8. Describe the protection of the various openings from the throat
during the action of swallowing.

9. Define peristalsis. Discuss the importance of peristalsis in the
digestive process.

Supplementary Readings

Howell, Wm. H., Textbook of Physiology (W. B. Saunders Co.).

Kimber, D. C, and Gray, C. E., Textbook of Anatomy and Physiology (The

Macmillan Co.).
Martin and Weymouth, Elements of Physiology (Lea & Febiger).

CHAPTER XIV

DIGESTION
AND ABSORPTION

Z'-^A*

mgmm

Large globules of fat.

Separated in an emulsion.

What changes does the food undergo in the stomach and intestines ?
What is the importance of gastric juice in digestion? How is the
small intestine adapted for carrying on digestive activities? What is
the importance of absorption?

The stomach. The esophagus ends in the stomach, a collapsible,
saclike enlargement of the alimentary canal, which serves as a
temporary receptacle for food. When contracted, the shape of
the stomach is comparable to a sickle blade or a sausage. When
distended with food, it is more pouchlike. The stomach has two
openings ; one where the esophagus joins it, known as the cardiac
opening, the other which communicates with the small intestine
and is known as the pylorus (gateway). Both the cardiac and
pyloric entrances are guarded by ringlike muscles known as
sphincters. These muscles contract and keep the openings closed,
except when food is passing through them. Food is kept in the
stomach until it is ready for intestinal digestion ; then the circu-
lar fibers guarding the pyloric valve relax.

The walls of the stomach are made of muscle and other tissues.
The inner coat (mucous membrane) of the stomach is honeycombed
by tiny, shallow pits, which are the openings or mouths of the
gastric glands from which the gastric juice is discharged. The
gastric or digestive juice is composed of water, hydrochloric acid,

125

126 DIGESTION AND ABSORPTION

and the enzyme, pepsin. The meat known as tripe is the lining
of a cow's stomach and somewhat resembles the lining of the
human stomach.

Problem. What is the effect of gastric juice on protein f

I. Prepare some very thin slices of hard-boiled white of egg. Put a slice
of this into each of four test tubes. Have the pieces alike in size. Add to the
four tubes the following liquids :

A. Water, to tube number one.

B. Water in which pepsin has been dissolved, to tube number two.

C. Water and very dilute hydrochloric acid, to tube number three.

D. Water, very dilute hydrochloric acid, and pepsin (artificial gastric
juice), to tube number four. Place all four test tubes and contents in a
warm place or in an incubator.

II. Compare the appearance of the egg in the four tubes at the end of one,
two, four, eight, and twenty-four hours. What effect have the various con-
stituents of gastric juice on protein ?

III. Give your explanation of the following :

A. When people are suffering from indigestion, why are pepsin and
hydrochloric acid sometimes prescribed ?

B. If there is too much hydrochloric acid in a person's stomach, why
is bicarbonate of soda sometimes prescribed ?

C. Why is it unwise for a person to take artificial gastric juice or
bicarbonate of soda unless a doctor definitely prescribes it ?

Problem. What is the effect of the size of protein food on the time
needed for digestion f

I. Place in a test tube some finely chopped white of egg. Put into an-
other test tube some larger pieces of white of egg, and into a third test tube,
some very large pieces of white of egg. Cover the egg white in each tube with
artificial gastric juice.

II. Compare the appearance of the egg in the three tubes, hour by hour,
and note the results.

III. What do you find to be the relation of the size of food to the time
needed for digestion ? Of what value is thorough mastication of food ?

SECRETION OF GASTRIC JUICE

127

Problem. What animal proteins are digested most quickly and most
thoroughly f

I. Put into separate tubes equal-sized, thin slices of the following proteins t

A. Well-boiled beef. • D. Roast pork.

B. Raw beef. E. Roast lamb.

C. Roast beef. F. Fried fish.

Pour an equal amount of the artificial gastric juice into each tube. Place
the tubes in a warm place.

II. Compare at regular intervals the amounts of protein in each tube.

III. State your conclusion from your observations.

opening into
the stoiScNtK-

Secretion of gastric juice. The secretion of gastric juice is
continuous. Even when one is not eating there is a small amount
of secretion, but during
the act of eating and
throughout the entire
period of digestion, the
rate of secretion is greatly
increased. This rate is
regulated by several fac-
tors : (1) Psychical stimu-
lations are brought about
by the sensations of eat-
ing. The taste and odor
of food stimulate the be-
ginnings or receptors of

Certain Sensory nerves Sit- In a gastric gland certain cells secrete pepsin, while

certain others secrete hydrochloric acid. With water,

Uated in the mouth and these substances are the main constituents of gastric

rr , 1 . . . juice which is emptied from the gland into the stomach.

nose. Inis stimulation

results in activating the gastric glands. It has been demon-
strated, experimentally, that as soon as a dog tastes, smells, or
sees food, the flow of gastric juice increases. A psychic stimu-
lation results in a copious flow of gastric juice. Such a stimula-
tion is always brought about when one eats appetizing food.

cells -which
secrete ^ . . _
fluid containing
pepsin^

neclc of
glctncl!

the^khC

128 DIGESTION AND ABSORPTION

(2) Chemical stimulation is brought about by the materials con-
tained in certain foods and by the stimulating materials contained
in the products of digestion. Certain foods such as meat juices
or extractives, by their actions upon the nerves of the stomach,
stimulate the gastric glands to pour forth their secretion. Such
substances are called secretagogues. Other foods such as milk and
bread do not seem to contain these substances. When these foods
are eaten, the secretion of juices is probably due to a mechanical
stimulus resulting from the presence of food in the stomach. When
certain digestive products are formed, they, in turn, stimulate a
further secretion of gastric fluid. The amount of secretion de-
pends upon the quantity and nature of the food to be digested.

Gastric juice is a thin, nearly colorless liquid with an acid
reaction. It contains some inorganic salts, but the essential con-
stituents are hydrochloric acid and two enzymes, pepsin and rennin.
Hydrochloric acid in normal gastric fluid is found in the propor-
tion of 0.2 to .5 per cent. Experiments have shown that a higher
concentration of hydrochloric acid is not favorable for the diges-
tive action of pepsin. It has the following functions : (1) it acti-
vates the pepsinogen (an inactive form of pepsin) of gastric
juice to form pepsin; (2) it provides an acid medium which
is necessary for the pepsin to carry on its work; (3) it swells
the protein fibers, thus providing a larger surface for the action
of pepsin; (4) it kills many bacteria that enter the stomach;
and (5) it helps to regulate the opening and closing of the pylorus.

Pepsin, which may be called gastric protease, is first formed by
the gastric glands as pepsinogen and is changed into pepsin when
it comes into contact with the hydrochloric acid. It has the
power of changing proteins into the intermediate products called
proteoses and peptones. These are a simpler form of proteins, but
not yet simple enough to be absorbed. Therefore, they are called
intermediate products of digestion.

Rennin, another enzyme found in gastric juice, acts upon casein.

SECRETION OF GASTRIC JUICE 129

the protein of milk. It converts this substance into a clotted mass,
the curd. The pepsin carries on the digestion of curd more effi-
ciently in this form than it ^.Car^ioc ojxming-|
could in the original form. y\

Food is kept in constant Y^|l--'Fun^.us

motion in the stomach. J?? 4?

By means of the action of ^ jt: \*y
the stomach muscles, food ^w^^v' lorus ^
is churned back and forth

, , , ., . The diagram on the left shows the shape of the

and Up and dOWn Until it stomach when empty; and the one on the right shows
i i , in the approximate shape after a hearty meal.

is reduced to much finer

particles than were formed in the mouth. The partially digested
food is in liquid form and is called chyme. The reduction of the
food into these very fine particles is invaluable in increasing the
amount of food surface to be exposed to the action of digestive
juices in the small intestines. The cardiac sphincter prevents the
return of food to the gullet during the churning process. At
intervals the pyloric sphincter opens and some of the chyme is
forced into the small intestine by a wave of contraction.

The stomach acts as a reservoir, holding the food and feeding it
at regular intervals to the small intestine. The time required for
gastric digestion of a meal depends upon the quantity and kind of
food eaten. An average meal requires about five hours for gastric
digestion. Solid particles tend either to keep the pyloric valve
closed, or to force it to relax, because of fatigue, before the food
has reached a semi-fluid condition. It is largely the acidity of the
chyme that causes the relaxation of this valve, but in the small in-
testine the acid has just the opposite effect. When the acidulous
chyme passes into the intestine, it causes the sphincter to contract.
The pylorus then remains closed until the acid has been neutral-
ized by the alkalinity of the intestinal juice. Since few enzymes
are produced in the stomach and their digestive action is incom-
plete, the digestion of the nutrients continues in the small intestine.

130

DIGESTION AND ABSORPTION

/ft—

The salivary digestion of starch continues in the stomach until
the acid permeates all parts of the food mass. Proteins are the

nutrients chiefly affected
in gastric digestion, but
even their digestion is
incomplete. Many bac-
teria that enter with the
food are killed by the
germicidal action of the
hydrochloric acid.

The small intestine.
The small intestine is a
narrow, tubular organ .
about one inch in diam-
eter and from twenty to
thirty feet in length. It
is so coiled that it easily
fits into the central part
of the abdominal cavity. It is continuous with the pyloric end of
the stomach. A membrane, the mesentery, attaches the coils of
the intestine to each other and to the backbone.

The small intestine has muscles which permit two kinds of
movement, one called rhythmic segmentation and the other peri-
stalsis. The rhythmic segmentation is caused by local constric-
tions of the intestinal wall at regular intervals. These constrictions
divide the chyme into a number of equal parts. Within a few
seconds, each of these portions is halved and unites with the cor-
responding halves of the adjacent segments. In the next con-
striction the segments are restored to their original position. This
enables the mass to be thoroughly mixed with the digestive juices.
Then a peristaltic movement, a succession of waves of contraction
and relaxation, beginning at the anterior end of the small intestine,
sweeps along, forcing the food onward through the tube.

Rhythmic constrictions of the walls of the small in-
testine break the food into equal segments. Each of
these segments is halved and unites with the adjacent
half of the next segment. Segmentation continues, in-
suring the complete mixture of digestive juices and food.

THE PANCREAS 131

•

Certain glands in the lining of the intestine secrete a juice called
succus entericus or intestinal juice. Near the region where the
small intestine leads from the stomach is the opening of a duct
formed by the union of ducts from the liver and pancreas.
Through this duct, juices from the liver and pancreas are emptied
into the small intestine, where they mingle with the secretions of
the intestinal glands.

The pancreas. The pancreas is a flat, pear-shaped gland, about
five inches in length, that lies slightly back of the stomach, between
the lower part of the stomach and a fold of the intestine. It
secretes an alkaline digestive juice called pancreatic juice. This
juice contains three enzymes : (1) An amylase, amylopsin, similar
to the ptyalin of the saliva, continues the conversion of starch
into simple sugars. (2) A protease, formed as trypsinogen, is con-
verted into trypsin by the action of a substance, enterokinase,
secreted by the mucous membrane of the small intestine. Tryp-
sin, similar to, but more powerful than pepsin, changes the pro-
teins into the simpler products, peptones and amino-acids. (3) A
lipase, steapsin, breaks down fats into fatty acids and glycerol.
Some of these fatty acids then combine with the alkaline salts,
present in the juices of the intestine, to form soaps. Fats are
insoluble, but these soaps are readily soluble in water. Soap-
making, saponification, is part of the digestive process. The
breaking down of the fats and the saponification that follows are
made easier by emulsification, that is, the breaking up of the fat
into very tiny particles.

Problem. What is the effect of an alkali on a fat ?

Place in each of two test tubes a small amount of olive oil. Add an equal
amount of sodium hydroxide (an alkaline material) to the oil in one of the
tubes. Let it stand for forty-eight hours, shaking occasionally.

I. What difference do you observe between the oils in the two test tubes ?
The change you have brought about in the one is called an emulsion.

II. Mount a drop of oil under the microscope.

132

DIGESTION AND ABSORPTION

liver

III. Mount a drop of the emulsified oil under the microscope.

A. Describe the difference in the appearance of the two drops of oil.

B. Why would you expect emulsification to hasten the digestion of fats ?

IV. Bile and succus entericus are alkaline liquids. What effect would you
expect them to have on the digestion of fat ?

The liver. The liver is the largest gland in the body. It is
situated on the right side of the body, and covers part of the

stomach, small intestine,
and large intestine. The
upper surface fits closely
into the under surface
of the diaphragm. The
liver secretes an alkaline
juice, yellowish-green or
brown in color, called
bile. This pours, by
means of the bile duct,
into the small intestine
only during the period
of digestion. The alkali
in the bile activates the
digestion of fats and helps in the absorption of digested fats. The
excess bile passes through another duct into the bile sac or gall
bladder, where it is stored until needed. Sometimes a part of
the bile substance crystallizes in this duct, forming gallstones.
In such a case, the bile duct is closed and the excess bile passes
into the blood, causing jaundice.

Intestinal digestion. The presence of food in the small intes-
tine stimulates the flow of intestinal juice which contains a num-
ber of enzymes. An intestinal protease, erepsin, helps to convert
the proteoses and peptones formed in the stomach into the end
products of digestion, amino-acids. Several inverting enzymes
in the intestinal juice convert the double sugars into single or

Common
bilc'&uct

Common
bile
panate
dxccX.

intestine;

Not far below the stomach, a tube empties into the
intestine. This tube leads from the pancreas, the liver,
and the gall bladder, and drains juices into the intestine.

INTESTINAL DIGESTION

133

simple sugars. Some of these enzymes complete the digestion of
starch and sugar which was started in the mouth. Another con-
stituent, enterokinase, causes the trypsinogen of pancreatic juice
to form trypsin. There is also an active hormone, secretin, in the
intestinal juice. It has no digestive action but passes into the
blood stream and is carried to the liver and the pancreas, which
it activates. (A hormone is a chemical substance formed in one
part of the body and activating another part.) It has been
found that if a dog is fed and some of its blood in the vein lead-
ing from the intestine is introduced into the blood of another
dog, the liver in the second dog immediately secretes a large
amount of bile, and the pancreas secretes pancreatic juice, which
shows that a hormone must have passed through the blood
and was carried to the pancreas and the liver. In the human
body, most of the food is digested in the small intestine because
the food stays there longest. It has been estimated, from obser-
vations, that the last food of
a meal passes out of the small
intestine about ten hours
after eating. There are more
enzymes in this part of the
digestive tract than in any
part of the canal, which, also,
accounts for the large amount
of digestion that occurs here.
The large intestine leads
from the small intestine. It
is about five feet long, and
about two and one half inches
in its broadest part. A little
pouch is formed where the large intestine connects with the small
intestine. Leading from this pouch is a short, narrow, wormlike
tube, usually less than the diameter of an ordinary lead pencil,

inteetaYier

vermiferrru

Enough of the small intestine and large intes-
tine are shown to make clear the position of the
appendix. Note the opening of the appendix.

134

DIGESTION AND ABSORPTION

CHART OF CHEMICAL DIGESTION

Digestive
Gland or
Glands

Juice

DlGESTANT 1

Place of

ACTION

Substrate 2

End Product 8

Salivary

Saliva
(alkaline) 4

Amylase
(ptyalin)

Mouth and
stomach

.Starch

Dextrins and
maltose

Gastric

Gastric
(acid)

A. Protease
(pepsin)

B. Rennin

C. Hydro-
chloric
acid

Stomach

A. Protein

B. Casein
of milk

Q. Mineral
matter .

Pepsinogen

A. Proteoses and
peptones

B. Curd

C. Solution of
mineral
matter
Pepsin

Pancreas

Pancreatic
(alkaline)

A. Protease
(trypsin)

B. Amylase
(amyl-

Small
intestine

A. Proteins

B. Starches

■ • • .lapTi

A. Amino-acids

B^ Dextrins and

*mm£p maltose

'C. Fatty acids
and glycerol

D. Soaps

opsin) * —

C. Lipase
(steap%^an».
sin) *

D. Alkaline
salts

■'■

C. EmulsifleV
fats

D. Fatty acids

Liver

Bile
(alkaline)

Alkaline salts

Small
intestine

Helps to emulsify fats; saponify fatty
acids forming soaps. These soaps
emulsify more fats.

Intestinal

juice

(alkaline)

A. Entero-

kinase

B. Protease
(erepsin)

C. lnvertases

a. Maltase

b. Sucrase
o. Lactase

D. Alkaline
salts

Small
intestine

A. Trypsin-
ogen

B. Proteoses
and pep-
tones (from
stomach)

a. Dextrins
and maltose

b. Sucrose
0. Lactose

D. Fatty acids

A. Trypsin

B. Amino-acids

glucose

6. Glucose and
fructose

o. Glucose and
galactos

D. Soaps

1 Digestant is a term used to designate a chemical material which brings about a change In the digestive process.

2 Substrate is a term used to designate the material changed in the process of digestion.

8 End product denotes the product at the termination of the particular process considered. This product may

or may not be ready for absorption.
* There is a maltase in saliva which converts small quantities of maltose into glucose.

THE LARGE INTESTINE 135

called the vermiform appendix. It has no useful function. If
food collects in the appendix, it is not easily drained out. This
food may decay, which causes an inflammation commonly known
as appendicitis.

The large intestine is divided into the ascending colon, trans-
verse colon, descending colon, and sigmoid flexure (see page 119).
The colons and the sigmoid flexure inclose the folds of the small
intestine. The sigmoid flexure ends in the rectum. The rectum
is six to eight inches long and leads into the anal canal, having
an external aperture, the anus. This opening has an internal
sphincter muscle of the involuntary type, and an external sphinc-
ter that is voluntary. These sphincters control the passage of solid
waste from the body.

The process of digestion is continued to a slight degree in the
large intestine, due to the presence of the digestive fluids with
which the food became mixed in the small intestine. The indi-
gestible waste materials associated with all foods, are removed
from the body through the large intestine by means of peristaltic
.movements. The chief waste product is the cellulose of vegetable
food and the fiber of meat.

Bacteria are abundant in the large intestine. They cause the
putrefaction of unabsorbed proteins. Some of these products of
putrefaction are absorbed from the intestine by the blood, while
the others are eliminated from the body. If an excessive amount
of toxic products from this putrefaction is absorbed into the blood,
a headache or feeling of lassitude will usually result. Normally,
the rectum is empty until just before defecation or the elimination
of solid waste.

ABSORPTION

After foods have been refined, split, and standardized in the
digestive process into the simplest forms; namely, amino-acids
from proteins, glucose and galactos from carbohydrates, and fatty

136

DIGESTION AND ABSORPTION

acids, glycerol, and soaps from fat, they are in a diffusible form
and may enter the blood where they will be utilized. The process
of food passing through the lining of the alimentary canal and
through the walls of the blood vessels is called absorption. Ab-
sorption is a process of osmosis. Very little absorption takes place
in the mouth, throat, gullet, and stomach because the food is in
mm *&z ■"' constant motion, and because very

little of it has reached the end
point of digestion.

Most absorption takes place in
the small intestine for the follow-
ing reasons: (1) The digestion of
most of the food has been com-
pleted. Many of the end products
of the digestive process are formed
in the small intestine. (2) The
great length of the small intestine
gives a larger absorbing surface.
(3) The small intestine is narrow
and the food is pressed against all
its surfaces. Consequently, not only the lower surface but all its
surfaces are used in the absorbing process. (4) Muscular activity
helps the food to mix with the digestive juices so that complete t
digestion takes place. At the same time, the food is pressed against
the absorbing surface. (5) There are special adaptations, folds,
and villi, for increasing the absorbing surface. The length of the
small intestine is at least twenty feet in an adult. The number
of epithelial cells used in absorption is tremendously increased by
the presence of circular folds or ridges around the circumference of
the lining of the intestine. On these ridges are little structures
called villi, so numerous and so close together that they resemble
the nap on carpet. Each villus consists of an outer layer of epi-
thelial cells inclosing a network of capillaries and a central lymph-

Hairlike microscopic structures known
as villi are found in great numbers on the
lining of the small intestine. They in-
crease the absorbing surface. The mouths
of intestinal glands show among them.

ABSORPTION

137

pillar^

mucus cell

..lacteal

channel called a lacteal. The spaces among the capillaries, lac-
teals, and epithelial cells are filled with fluid known as lymph.
The digested food is absorbed
by osmosis through the epithe-
lial cells of the villi. These villi
cells exert a selective action, per-
mitting only the passage of cer-
tain materials. The process of
osmosis here is an active not a
passive one. Some soluble salts
are readily absorbed, while
others like tartrates, citrates,
and calcium salts cannot pene-
trate the epithelial cells. Fatty
acids, glycerol, and soaps enter
the epithelial cells, and during
the process of passing through
them are change back into fat
particles. This fluid or lymph
then passes into the lacteal s and
through other lymphatics,
leading from the lacteals,
and eventually drain into
the blood system. The
amino-acids, simple sugars,
salts, and water pass di-
rectly from the epithelial
cells of the intestine into
the capillaries and thus
become part of the liquid
portion of the blood.

The adaptations of the
small intestine are so adequate that practically everything dif-

orfcery

—vein.

The villus is adapted for absorption. A network of
microscopic blood vessels absorbs digested food from the
small intestine. A lymphatic, known as a lacteal, rims
through the center and takes in the digested fat.

WH. FITZ. AD. BIO.

138 DIGESTION AND ABSORPTION

fusible has been absorbed by the time the residual material enters
the large intestine. This material consists chiefly of indigestible
substances and some water. The water is gradually absorbed
during the progress of the chyme along the large intestine. This
results in the waste material becoming more and more pasty as it
approaches the rectum for elimination.

Hygiene of digestion. The body is normally in a state of health
and not disease. It is abuse of some kind that induces digestive
disturbances commonly called indigestion. Hygienic habits of
living make for good digestion. Activity in the open air and sun-
light, good food, relaxation, and rest are of prime importance.
Proper nutritional habits should, be established. Meals should
be taken at regular intervals. If the digestive organs are worked
periodically, more regular digestive habits are established. As a
rule, food should not be eaten between meals, for it disturbs the
physiological routine and, also, interferes with the appetite.

Since the alimentary canal is composed largely of muscles, exer-
cise is invaluable in keeping these muscles in proper tone. By
tone we mean the constant and unconscious tendency of the
muscles to contract under normal conditions. However, strenuous
exercise immediately after a meal is bad, as it withdraws much of
the blood from the digestive organs where it is needed, and sends
it to the active skeletal muscles that are working. This may re-
sult in indigestion and possibly muscular cramps. Consequently,
neither maximum digestion nor proper muscular activity is ob-
tained. This is one reason why persons are subject to digestive
or muscular cramp if they swim too soon after eating a heavy
meal. For a similar reason, undue excitement or mental stress
should be avoided during or after meals. Since the stimulation
of digestive glands is partly psychic (mental), violent emotions in-
terfere with the proper flow of digestive juices and withdraw the
blood from the digestive organs and send it to the brain and
nervous system. Pavlov, a famous Russian physiologist, learned

HYGIENE OF DIGESTION 139

through scientific experimentation, that, in dogs, fear, anger, and
rage interfered with proper digestion and altered the character of
the digestive juices.

Food should be thoroughly chewed to be properly mixed with
-the saliva. As much water as possible should be taken each day.
There is no objection to drinking water with the meals, providing
that it is not so cold that the organs might be chilled, and that the
food is thoroughly masticated and not washed down by the water.

As the undigested part of the food passes through the colon,
it gradually loses its water through the process of absorption.
This waste becomes semisolid. It should be removed daily at
a regular time. If this defecation does not take place because of
haste, or inconvenience, or some irregularity in the routine, the
water in the solid waste becomes absorbed and the waste be-
comes so compact that it is difficult and in some cases impossible
to eliminate. A cathartic or laxative must then be taken to stimu-
late the activity of the intestinal movement. It is a well-known
fact that improper foods may cause constipation. This condi-
tion may be avoided by eating bulky foods which will stimulate
the work of the muscles of the canal. Such bulky foods are
vegetables, salads, and fruits. Proper routine, including regu-
larity of meals and regular times for elimination of wastes, must,
also, be established.

Laxatives are useful in removing an acute condition of constipa-
tion but should not be taken regularly. Some laxatives contain
drugs that stimulate the nerves controlling the muscles used in
defecation. Other laxatives called the salines contain the salts
of sodium, potassium, and magnesium. They cannot be absorbed
by the intestine. They hold a great deal of water in solution and
increase and soften the bulk of the material, favoring its move-
ment along the canal. Epsom salts, magnesium citrate, and so-
dium phosphate are examples of saline cathartics. A third type
of laxatives is heavy oil, mineral or castor oil. These line the food

140

DIGESTION AND ABSORPTION

tract with a film of oil. The oil tends to soften and increase the
bulk of the intestinal content.

The best ways of preventing and overcoming constipation are :
to act on the desire for defecation, to have a regular time for

<3?.T*.

830TM •Mifc.nigHC

6i>.>r

As digestion takes place, food is gradually absorbed until the wastes only enter the large in-
testine. When these wastes reach the rectum, they are ready for elimination. It takes about
twenty-four hours for digestion to be completed and for the wastes to reach the rectum.

doing this, and to eat plenty of fruit and vegetables, as these tend
to promote peristalsis.

Some investigators think that one of the contributing factors to
old age is the toxins absorbed from putrefaction in the large intes-
tine. The toxins affect the arteries causing the hardening of the
arterial walls. The bacteria of putrefaction work best in an alka-
line medium. A Russian physiologist, Metchnikoff, conceived the
idea of introducing an acid into the large intestine. He thought
this would check putrefaction and possibly postpone old age. He
observed that Bulgarians who used a great deal of sour milk, live
to a greater age than other people. He knew that the' acids from
most foods are neutralized before they reach the large intestine,
but that unlike ordinary sour milk the acid in Bulgarian milk
does reach the large intestine. Different strains of bacteria in
milk cause the two different reactions. Bacillus bulgaricus and
bacillus acidopholus which is a related strain of microorganisms,
have been cultivated in America. Experiments are now being
made with acidopholus milk to determine whether it does have a
beneficial effect although there is as yet no definite proof.

People should not become faddists in eating. Nutritional

HYGIENE OF DIGESTION 141

rules established by proper authorities should be followed. If
one suffers from overweight or underweight, his diet should be
regulated professionally and not by quack methods. All kinds of
diets are in vogue; namely, milk diets, raw-food diets, cooked-
food diets, vegetable diets, and fruit and nut diets. As a rule,
most, if not all of these, should be questioned and avoided by
the average person unless a competent physician has done the
prescribing. Otherwise, a diet might be selected that would be
detrimental rather than beneficial in many instances. The use
of patent medicines of all kinds should usually be avoided. Some
people decide they have too much acid in their systems and take
an alkali like bicarbonate of soda to counteract it. In many cases,
bicarbonate of soda stimulates the production of more acid.
Others decide they lack gastric juice and buy artificial gastric
juice or pepsin and hydrochloric acid to aid digestion. This may
interfere with the proper production of natural gastric juice. Still
others believe a physic taken once a week is invaluable. This
may get the system so used to drugs that in time it will not be
able to function without artificial stimulation. Headaches, due
to digestive disorders, are cured by getting rid of the cause of the
disturbance, not by headache powders.

Briefly stated, normal digestion is our heritage. If habits of
eating the proper foods and defecation are regular, digestion will
usually be normal. The best way to clear up indigestion is to find
out the cause of the irregularity and correct it.

Questions and Suggestions

1. If the kinds or classes of enzymes are amylases (starch-split-
ting), proteases (protein-splitting), and lipases (fat-splitting), classify,
in their right classes, all the enzymes that you have studied.

2. Discuss the different causes for the stimulation of the flow of
digestive juices.

3. Discuss the importance of peristalsis in eliminating the solid
wastes of the body.

142 DIGESTION AND ABSORPTION

4. Locate four sphincters and discuss the importance of each.

5. Plan an experiment which will illustrate the digestion of
starch.

6. Name three intermediate and three end products in the digestion
of nutrients.

7. Discuss the importance of the villi in absorption.

8. Give two classes of cathartics or laxatives. After reading the
labels of two or three common cathartics, state to which class each
belongs.

9. Name an unhygienic condition that is frequently found among
high school students and which may lead to digestive disorders.

10. What is the objection to reading and eating at the same time ?

11. Name two scientists who have investigated food habits. Dis-
cuss their contributions to the science of nutrition.

12. Review and report on the digestion and osmosis experiments
set up in elementary science.

Supplementary Readings

Haggard, H. W., Science of Health and Disease (Harper & Brothers).
Kimber and Gray, Textbook of Anatomy and Physiology (The Macmillan Co.).

CHAPTER XV

BLOOD AND ITS
IMPORTANCE

William Harvey.

Vesalius' idea of blood vessels.

What is the relation of blood to the other tissues of the body? Where is
blood made and where are its various parts destroyed? What is meant
by different types of blood? What is the imjwrtance of blood tests?

Many cells are far from the source of supply of food and oxy-
gen and far from the organs which will excrete their wastes.
The blood, therefore, acts as a medium for the distribution of
food materials and oxygen to the cells, and for the collection of
wastes from the cells.

Circulation is the ceaseless movement of blood through the
body in a system of closed tubes called blood vessels which branch
to all parts of the body. When blood flows from any. part of the
body, blood vessels have been broken.

Problem. Study of the blood.

Secure some freshly drawn blood from a butcher or slaughterhouse. Keep
in a tightly corked bottle when not in use.

I. Pour two or three ounces of the blood into an open dish and beat it
vigorously with a few broom straws.

A. Describe the nature of the material removed by this beating. This
material is called fibrin. As the beating exposed the blood to the air,
the liquid blood protein, fibrinogen, was converted into the solid form,
fibrin.

B. Describe the material left in the dish. This is defibrinated blood.

143

144 BLOOD AND ITS IMPORTANCE

II. Continue beating until no more fibrin can be removed.

III. After beating, remove the fibrin, and pour the remainder of blood
into a bottle. Label it defibrinated blood.

IV. Pour a like quantity of unbeaten blood into a second bottle and let
both volumes of blood stand, corked, for several days. Compare the appear-
ance of the materials in the two bottles.

A. Describe any solid mass, a clot, which may have formed in one or
both bottles.

B. Describe the liquid around the clot. This liquid is called serum.
Compare blood serum with defibrinated blood.

V. Place an ounce of blood in a third bottle and, by means of a delivery
tube, add oxygen to it.

A. What effect has oxygen on the color of blood? This is now oxy-
genated blood. It may be compared to arterial blood.

VI. Place an ounce of blood in a fourth bottle and, by means of a delivery
tube, add carbon dioxide to it.

A. What effect has carbon dioxide on the color of blood? This is
deoxygenated blood. It may be compared to venous blood.
"VTI. Look at the veins in your wrist.

A. Do veins appear to have oxygenated or deoxygenated blood in
them?

B. Explain why blood which flows from a cut vein looks like oxy-
genated blood.

Problem. Study of blood serum.

Test the serum for protein, starch, sugar, fat, water, and mineral matter.
Account for the presence or absence of each.

Problem. Study of blood corpuscles.

Mount a tiny drop of blood on a glass slide. By means of the edge of a
square cover glass, smear the drop across the slide, making a thin film. Cover
with Wrights' Blood Stain for three minutes ; then wash off the stain. Exam-
ine with low power and then with high power of the microscope. Observe the
regular, disklike, yellowish cells which cling together ; when in masses of great
numbers they appear red. These are the red corpuscles. The larger, irregu-
lar, blue cells are the white corpuscles. When unstained, they are colorless.

I. Estimate roughly, the proportionate number of the two types of cor-
puscles.

COMPOSITION OF THE BLOOD 145

II. Suggest a reason for calling the white corpuscles the amoeboid cor-
puscles ?

III. State three structural differences between the red and white corpuscles.

IV. What functions did the Amoeba perform with its pseudopodia ? Cer-
tain white corpuscles can, in a similar manner, engulf bacteria. These bac-
teria are then digested by the white corpuscles and are thus eliminated from
the blood.

Composition of the blood. Blood may be called a tissue.
It consists of a yellowish liquid, the plasma, and cellular particles,
the red and white corpuscles and blood platelets. The plasma
is a clear fluid containing fibrinogen and other blood proteins,
nutrients, and wastes. Some of the proteins in the plasma are
peculiar only to the blood. Little is known of the use of these,
with the exception of fibrinogen. The use of fibrinogen, which was
transformed to fibrin in our laboratory exercises, will be discussed
later. Amino-acids are also a part of the blood plasma. These
amino-acids are digested proteins which are called building stones
of the body. They are distributed by the blood to the cells, and
they build protoplasm. Fat, glucose, water, and mineral matters
are also taken in by the plasma from the alimentary canal. More
than 80 per cent of the plasma is water. There is from 0.07 to 0.15
per cent each of fat and glucose. The proteins constitute from
6 to 8 per cent of the plasma.

All of the food that is digested and absorbed does not circulate.
It is either used or stored in cells and gradually returned to the
blood as tissue cells require it. Animal cells can store fat and
starch, but very little protein. Therefore, any extra protein eaten
tends to be broken down and eliminated. Secretions from ductless
glands are absorbed directly into the blood. These liquids circulate
through the body, activating, inhibiting, or regulating the more
remote parts.

Oxygen is taken from the lungs by the red corpuscles of the
blood. The wastes, carbon dioxide, water, and urea, collected from

146 BLOOD AND ITS IMPORTANCE

the different cells as the blood circulates, are dissolved in the
plasma and carried to the kidneys, lungs, or skin, where they are
thrown out.

There are various kinds of white corpuscles. When stained, one type, the polymorphonu-
clear, shows nuclei with one, two, three, four, or five enlargements. In health there is a
definite relationship of the numbers of each of the above; in starvation or disease the fours
and fives are seldom found. Blood tests usually indicate the general condition of the body.

Chemical substances in blood, known as antibodies, help to com-
bat germs directly, or neutralize the toxins which the bacteria
secrete in the blood. These substances are produced by the cells
during a disease or infection. Immunity to disease, which will be
discussed later, is brought about in the body by these antibodies.

Blood a tissue. Red corpuscles were mentioned when tissues
were considered. They are five to seven hundred times as numer-
ous as the white corpuscles. Present investigations show that they
differ from other cells in that they lack a nucleus. They are made
from living cells located in the blood-forming tissue of the mar-
row of bones. Millions of these corpuscles are formed and given
off into the blood each minute. They are thought to gradually
disintegrate as they move about. The final destruction of the
small fragments probably takes place chiefly in the spleen and the
liver, but may occur in any part of the blood system. The correct
functioning of the red corpuscles depends upon the haemoglobin
which is the oxygen-carrying pigment of the blood.

A serious decrease in the number of red corpuscles or a deficiency
in haemoglobin in the corpuscles causes a condition known as
anaemia. Certain types of anaemia in people have been treated
successfully by a liver diet. The liver which is used as food
probably contains iron gotten from destroyed corpuscles. This
form of iron seems to be more valuable than the iron com-
pounds in medicines used for treating anaemia. The body seems

BLOOD AS A TISSUE 147

to be able to assimilate it better. Whether the liver diet is reme-
dial because of the iron present, or whether there is a vitamin
present that stimulates the body to make more red corpuscles,
has not yet been conclusively proved. In order to determine
whether a person has anaemia, a drop of blood is put on a slide
which is divided into sections by marks etched on the surface.
These spaces are called counting chambers. The number of red
corpuscles are estimated in relation to the white corpuscles present.
This is called a blood count. If there are too few red corpuscles
in relation to the white corpuscles, the person is said to be anaemic.
There is also a color scale used to test for anaemia.

The haemoglobin in the red corpuscles readily unites with oxy-
gen and forms an unstable compound, oxyhaemoglobin. When
the oxygen-carriers pass cells deficient in oxygen, the oxyhaemo-
globin will give up its oxygen supply. The red corpuscles of man
are smaller than the red corpuscles of nearly every other animal.
This allows a greater number per given volume and gives a greater
absorbing surface. Thus these numerous small corpuscles carry a
greater supply of oxygen than if they were larger.

The white corpuscles are larger and less numerous than the red
corpuscles. Because they are capable of independent motion,
they can force their way among the cells, which make up the walls
of capillaries, and escape into surrounding tissues. Certain of the
white corpuscles, by means of their protoplasmic processes, en-

White corpuscles can make their way among the cells in the walls of capillaries by their inde-
pendent motion. They may be found in tissues where they can attack invading bacteria.

gulf the bacteria in blood and other tissues, and digest them.
These are the phagocytes and the process is phagocytosis. It is
thought that white corpuscles originate in lymph nodes and in the

148

BLOOD AND ITS IMPORTANCE

spleen through mitotic division. When an infection occurs in the

body, they multiply in great numbers and later disintegrate or

probably escape from the blood upon mucous surfaces, especially

, , in the intestine. When

lympK

°*v££ en

oxjrg&tv

The cells take oxygen carried by the red corpuscles
and use it to burn food for the release of energy.

white corpuscles are de-
stroyed by bacteria, the
dead corpuscles are called
pus. An abnormal in-
crease of white corpuscles
in the blood usually indi-
cates the seriousness of
the infection and the
amount of resistance of-
fered by the body.
Blood clotting. Blood platelets are tiny bits of protoplasm
found in blood. They are small cells, but lack a nucleus. Their
origin is probably similar to the red corpuscles. They are con-
cerned with blood clotting which takes place when blood is exposed
to air because of wounds or hemorrhages. Blood platelets dis-
integrate and give rise to a substance which plays an important
part in the change of the liquid protein, fibrinogen, always present
in blood, to a solid form, strands of fibrin. Calcium, also present
in blood, is involved in the precipitation of the fibrinogen. The
strands of the fibrin entangle the blood cells and form a jellylike
blood clot. Bleeding may thus be stopped. The body then re-
pairs, by building new cells, the blood vessels from which the blood
is flowing. People whose blood does not clot in the normal length
of time or who bleed profusely even from the slightest wounds are
called bleeders. The disease is haemophilia and it is usually
hereditary.

Blood grouping. The composition of human blood is constant
with the exception of the oxygen and carbon dioxide content.
But since the serum of one person may be injurious to that of

NECESSITY FOR CIRCULATION

149

another; four different groups of blood are now recognized. Under
ordinary conditions the body can renew blood as fast as it is needed.
However, in certain diseases and in cases of severe hemorrhages
it is necessary to introduce a quantity of blood into the veins of
the patients. In such cases, blood of a similar group must be
transfused, or results may be fatal through the dissolving of the
corpuscles, and a consequent release of a foreign haemoglobin.
Therefore, doctors always test a donor's blood to make sure it is
of the same group as the patient's before making a transfusion.

Necessity for circulation. Each cell in the body has work to do.
This work is performed through energy released in the cell. We
have already learned that glandular cells use chemical energy,
muscular cells use mechanical energy, and nerve cells need nervous
energy. All of these forms of energy are obtained from the food.
When the food is oxidized in the body, the energy stored in the
food is released. Each cell must receive a supply of oxygen and
food. in order to carry on the oxi-
dation process with its accom-
panying release of energy. When
the food is oxidized in the cells,
carbon dioxide, water, and ni-
trogenous wastes are formed,
and must be removed. The
blood carries the oxygen and
food to the cells and removes
the wastes from them. Since
the white corpuscles combat
germs, the blood must carry a
continuous supply of these to
whatever part of the body that
needs them. At the same time other protective chemical sub-
stances, antibodies, must be carried to the places needing them.
As food is oxidized in various tissues, heat is released. A great

Wastes formed during oxidation reach the
blood by means of the process of osmosis.

150 BLOOD AND ITS IMPORTANCE

deal of heat is generated in active tissues such as muscular tissue
and the liver, and the surplus heat must be distributed to passive
tissues. Very little heat is generated in passive tissues such as
bone, so heat must be sent to them by the blood when needed.
The blood system may be compared to a hot- water system. The
muscles are like little furnaces in which burning takes place. This
heats the surrounding blood. As the blood circulates it radiates
heat to the tissues that need it, and thus keeps the temperature of
the body constant at ninety-eight and six tenths degrees Fahrenheit
(98.6° F.). When glands give off secretions and have no ducts for
draining the secretions, the blood absorbs them.

In brief, the functions of blood are nutritive, protective, and
excretory. When scientists can supply the same conditions to
tissues outside of the body as those provided by the blood, tissues
can be kept alive under experimental conditions outside of the
body. This was one of CarrelPs big achievements. He experi-
mented for many years before he was able to duplicate the con-
ditions outside of the body that were found in the blood. When
he succeeded in doing this, he was able to grow tissues outside of
the body. His work has been previously discussed on page 54.

Questions

1. Define* oxygenated and deoxygenated blood. ♦

2. What is defibrinated blood ?

3. Compare arterial and venous blood.

4. Compare the red and white corpuscles in appearance, size, num-
ber, and function. Where are they made and where are they de-
stroyed ?

5. Give six functions of blood.

6. Why does blood clot ; why is blood clotting necessary ?

CHAPTER XVI

CIRCULATORY
SYSTEM

An early drawing showing the
circulation of the blood.

Malpighi's drawing of circula-
tion of a chick embryo.

What are the paths of blood through the body? What causes the cir-
culation of blood f What is the relation of circulation to the cells?

Problem. The study of blood vessels. *

Anaesthetize a tadpole with a little ether. Place the tadpole in a Petri
dish in a little water so that the tail can be mounted under the low power
of the microscope. Do not keep the tadpole out of water more than ten or
fifteen minutes at one time.

I. Note the blood flowing up some blood vessels and down others.

A. Suggest a reason for the parallel arrangement of the blood vessels.

B. Suggest a function of the connecting blood vessels.

II. The large elliptical cells passing through the vessels are the red cor-
puscles.

A. What is the advantage of having corpuscles in the smallest blood
vessels pass cells in a single line ?

B. Compare the red corpuscles of the frog with those of man.

III. Look at the sun or at a very bright light. Note tiny particles passing
through a network of tubes in your eyes. These are the red corpuscles passing
through tiny blood vessels.

In the plant, a system of tubes called ducts and sieve tubes dis-
tributes cell sap. In the human body, a network of tubes makes
up the circulatory system for the distribution of blood throughout
the body. Materials must enter and leave the blood by means

151

152 CIRCULATORY SYSTEM

of osmosis, since the blood vessels are closed tubes. Blood sup-
plies the cells with building and fuel materials and collects wastes
from them ; therefore, some blood vessels must be tiny enough
to get near to all the cells. These microscopic blood vessels, the
capillaries, connect with larger and larger vessels, the arteries and
veins, until the largest arteries and veins attain a size of one half
inch in diameter.

Problem. Study of the heart.

Secure from the butcher, the heart of an ox or of any other large animal.
If the school is near a slaughterhouse, it may be possible to secure enough
specimens so that each group of four students may have one. Cut the hearts
longitudinally. (These hearts may be kept in formaldehyde for further study.)

I. Describe the covering of the heart (the pericardium) .

A. What is its purpose ?

B. Explain all adaptations for this purpose.

II. Count the number of chambers or spaces in the heart.

A. The upper spaces are the right and left auricles; the lower spaces,
the right and left ventricles. 'Describe the structure, location, and size of
auricles and ventricles.

B. Describe the structure that separates the left side of the heart from
the right side.

C. Find the movable flaps, known as valves, that separate the auricles
from the ventricles.

1. Describe the valves in the left side of the heart, including in
your description the number of flaps, method of attachment, and func-
tion. Observe and describe the valves in the right side.

a. When blood passes from the auricles to the ventricles, what
effect would you expect it to have On the valves ?

b. If blood attempts to pass from the ventricles to the auricles,
what effect would it have on the valves ?

c. What must be the normal direction of the flow of blood ?

III. Name the tissues that largely comprise the walls of the heart.

A. Compare the thickness of auricle walls with those of the ventricle.

B. Compare the thickness of the wall of the left ventricle with other
walls of the heart.

C. What is the relation of thickness of heart muscle to its activity ?

THE ORGANS OF CIRCULATION 153

IV. Find the large vessel coming up through the center of the heart. If
enough of it is still attached, it will be seen to curve around in back of the
heart. Put the wooden end of your needle through it.

A. Into what chamber does the needle penetrate ? This vessel is an
artery known as the aorta. It sends blood by means of branches to every
part of the body except the lungs.

B. Describe the walls of the aorta.

1. Suggest a reason why arteries hold their shape instead of col-
lapsing.

2. Suggest a reason why they were originally named arteries (aer
— air ; terin — to hold) .

V. Locate two large vessels leading into the right auricle. These are
two veins called the upper or superior vena cava and the lower or inferior
vena cava. They bring blood from all parts of the body, except the lungs, to
the heart.

A. Compare the walls of these veins with the walls of the aorta. Which
are capable of greater movement ? Why ?

B. What is a probable difference in function between the inferior and
superior vena cava ?

C. Suggest a reason why veins do not hold their shape when empty of
blood.

VI. Try to locate the pulmonary artery originating in the right ventricle
and the four pulmonary veins leading to the left auricle. The pulmonary
artery takes blood from the heart to the lungs ; the pulmonary veins convey
blood from the lungs to the heart.

A. Suggest a reason for the blood going to the lungs.

B. Suggest a reason for the blood returning from the lungs.

VII. Make a simple diagram of the heart and the blood vessels connecting
with it. Label right auricle, left auricle, right ventricle, left ventricle, septum
or partition, valves, aorta, superior vena cava, inferior vena cava, pulmonary
artery, and pulmonary veins.

VIII. Write a brief paragraph describing the structure of the heart.

The organs of circulation. The arteries, veins, capillaries, and
heart make up the circulatory system. Approximately in the
center of the chest cavity, with its apex pointing toward the left,
is the conical-shaped heart. It is a highly muscular organ pro-

WH. FITZ. AD. BIO. — 11

154 CIRCULATORY SYSTEM

tected from friction by the moist membranous pericardium which
covers it. The ribs and breast bone furnish protection against me-
chanical injury. Large blood vessels collect blood from all parts of
the body and return it to the heart ; others take blood from the
heart to all parts of the body. The heart tissue, itself, has an in-
dependent blood supply called the coronary circulation. When the
heart is cut longitudinally, it is found to consist of four chambers,
a left auricle, a right auricle, a left ventricle, and a right ventricle.
A thick muscular partition through the center of the heart sepa-
rates the left side from the right side. The auricles receive blood
from the veins and give it to the ventricles. The act of receiving
blood does not require much work, so the auricle walls have com-
paratively little muscle in them. The ventricles force the blood
into the arteries to all parts of the body. In order to ac-
complish this pumping, the ventricles have very thick muscu-
lar walls. The walls of the left ventricle are much thicker
than the walls of the right ventricle. They have to send
blood to all parts of the body while those of the right ventricle
merely send blood to the lungs. Separating the ventricles from
the auricles are trapdoor arrangements called valves. These
are made of very strong connective tissue attached by cords of
the same tissue to the ventricles. On the left side, there is a
valve with two flaps, and on the right side, a valve with three
flaps. The blood passes from the auricles to the ventricles, by
merely pushing against the valves. If the blood backs up during
the contracting of the ventricles, the valves fill up, close, and
prevent the return of the blood into the auricles. Thus the
blood is kept moving in only one direction.

Arteries. The tubelike blood vessels which carry the blood
from the heart to all parts of the body are called arteries. The
largest ones branch from the ventricles, and subdivide into smaller
vessels until a network of very fine tubes, practically microscopic,
is formed. These connect with the capillaries. The arteries can

VEINS

to K^clSL-

pulmonar

ARTEBIBS

to "heocol

.mesenteric
.renal

A diagram of the circulatory system in which the blood vessels containing arterial blood are
colored red, those containing venous blood are colored blue, and the lymphatics are yellow.
Note that, in general, only the arteries contain arterial blood, but the veins coming from the
lungs have received a new supply of oxygen and hence also contain oxygenated blood.

155

156 CIRCULATORY SYSTEM

usually be distinguished from veins and capillaries by the presence
of considerable muscular tissue in their walls. Early anatomists,
when dissecting bodies, found these tubes empty and thought
that they were supposed to carry air and therefore called them
arteries (air-tubes) . Even the smaller arteries have muscular walls
and can contract and relax. The aorta and its branches are full of
blood all the time. When the left ventricle contracts, the blood
cannot move forward into the comparatively narrow arteries fast
enough to make room for the new supply sent out by the ventricle.
But, due to the elasticity of its walls, the aorta can expand and
receive the incoming blood. The impulse of the blood sent into the
arteries by the ventricular contraction causes a wave of distention
to travel along the blood vessel. This wave of distention is called
the pulse. The pulse is the passive stretching and contracting of
the elastic tissue. If an increased amount of blood is sent to a
particular part of the body, at any time, the arteries can always
accommodate it because of the elasticity and muscularity of their
walls. The pulse may be felt wherever an artery comes near the
surface of the body. Most arteries are deeply embedded in other
tissues so that the pulse is not easily noted. Arteries run near
the surface in the wrists, neck, and temples. Probably the most
convenient place for taking a pulse is in the wrist.

Problem. Study of the pulse rate.

I. Place the middle finger of the right hand about two inches from the ball
of the thumb of the left hand, thus locating a pulse. Count the number of
beats felt per minute. This is called taking the pulse rate.

II. Run up and down stairs two or three times. Again take the pulse rate.

A. What effect has exercise on the pulse rate ?

B. Keeping in mind the fact that the walls of the heart and arteries
have large deposits of muscle and elastic fibers, give the reason for the
effect of exercise on the pulse rate.

C. Discuss the beneficial effects of exercise on the arteries.

D. If you get insufficient exercise, what effect would it eventually
have on the heart and arteries ?

CAPILLARIES

157

III. Lie down or sit quietly for two or three minutes. Again record the
pulse rate.

A. What is the effect of rest on the heart and arterial muscles ?

IV. What is the value of the arterial pulse ?

V. If more blood is needed in one part of the body than in another, how can
it be properly distributed ?

The normal pulse rate in men is seventy-two beats per minute, for women
seventy-six. The pulse rate is still higher in children. An abnormal pulse
indicates some sort of unusual physiological condition.

Capillaries. The capillaries are microscopic tubes found
among the cells of the tissues. These vessels are characterized
by a lack of muscular tis-
sue. Their walls are mem-
branous. They receive the
blood from the arteries
and send it to the veins.
Materials pass from the
blood through the thin
walls of the capillaries to
the cells in surrounding
tissues. The waste prod-
ucts in the lungs and
other parts of the body
pass into the blood from
which they are later dis-
charged. This inter-
change of products is
possible because of the
membranous walls of the
capillaries. The blood receives enough of an impulse from the
heart to keep it moving through the capillaries.

Veins. The veins receive the blood from the capillaries and return
it to the heart. The veins connected directly with the capillaries

Capillaries are so tiny and numerous that they
traverse the most minute parts of the body. The red
corpuscles pass through in practically single file.

158

CIRCULATORY SYSTEM

are very tiny in size,
them join together.

n TO n

Blood flowing through veins passes
valves. When these valves are
opened due to back pressure, the
blood finds other vessels, sometimes
smaller, to traverse.

They get larger and larger as numbers of
The largest ones empty into the heart.
Their walls are composed of elastic,
connective, and some muscular tissue.
There might be a back-flow of blood
in the veins were it not for the
valves that are found along the walls
of the veins. These open in the
direction of the blood flow which is
toward the heart. If blood tends to
flow back, they open, and prevent the
blood from moving in the opposite direction. These valves may
be seen if you let your hand hang down, and shut off the blood
supply by holding the wrist tightly. The blood will back up
against the mouth of the valves and open them. As blood fills
these valves, a slight distension of the vein will be noticeable. In
some older people, these valves are likely to thicken and show as
swellings on the body. Since so small an amount of muscular tissue
is present in the walls, very little muscular contraction is possible.
The movement of blood in

the veins is caused by the

heart which is aided greatly

by the valves in the veins,

by muscles, and by the

lungs. The network of

capillaries feeding the veins

increases the flow just as

tributaries to a river cause

the flow of water in the

river. As breathing takes

place, pressure on the large

veins in the chest is released. This causes the blood to flow up

through the veins. Skeletal muscles in all parts of the body

The valves in veins are like tiny watch-pockets. If
blood tends to flow back, the valves fill up and close
the passage; thus blood is kept moving in one direction.

COURSE OF THE BLOOD

159

One blood vessel leads directly into another. The structure of
their walls varies, however. The small, muscular-walled arteries
lead into the membranous capillaries which, in turn, lead into the
smallest of the veins.

squeeze the veins as they contract. This, too, forces the blood
onward. If a person is inactive . for a long time, the blood in
the veins becomes sluggish. When we sit still for too long a time,
we say a foot has
" gone to sleep."
Other signs of
discomfort may,
also, be evident
because the skele-
tal muscles are
not propelling
the blood through
the veins.

Course of the
blood. The sys-
temic circulation.
The circulation of the blood through the body is easily under-
stood and remembered if we keep in mind that the sequence
of organs is from the left ventricle, arteries, capillaries, veins,
and right auricle. Blood never returns directly to the same
side of the heart it left and the auricles do not connect with
each other, nor do the ventricles connect with each other.

The left ventricle contracts and sends the blood past the valves
into the large artery called the aorta. This, in turn, contracts
and sends blood through smaller and smaller arteries to all parts
of the body except the lungs. As the arteries get in among the
tissues of the body, the muscular tissue decreases until the walls
of the blood vessels consist of a single layer of cells. • These ves-
sels are the arterioles which terminate in the capillaries. After
giving up the needed materials to the cells through the walls of
the capillaries and collecting excretions from the cells, the blood
passes into tiny veins. As the small veins lead from the tissues
they join and increase in size until they form the two largest

160

CIRCULATORY SYSTEM

veins in the body. The veins from the organs below the heart
drain into the lower or inferior vena cava; the veins from
the organs above the heart, with the exception of the lungs,
lead into the upper or superior vena cava. Both of these large
veins empty into the right auricle. From there, blood passes
to the right ventricle. This completes the systemic circula-
tion. The systemic circulation enables the blood to supply
tissues with needed materials and collect excreted materials from
them.

The pulmonary circulation. The right ventricle contracts and
sends the blood into the pulmonary artery which divides into two
sets of branches, one set going to each lung. In the lungs, these
arteries get smaller and smaller until they lead into the capillaries
of the lungs. . The carbon dioxide, collected from the cells, is
given to the lungs and a new supply of oxygen is absorbed through
the capillary walls. The blood then travels through veins of in-
creasing size until it reaches the large pulmonary veins, which take
the blood to the left auricle. This is called the pulmonary or
lung circulation. The pulmonary circulation enables the blood to
give up the carbon dioxide and take in a new supply of oxygen.

The portal circulation.
As the blood passes
through capillaries in the
stomach and small intes-
tine it absorbs food that
has been digested and
standardized into end-
products. Were all this
collected food to circulate
until utilized the amounts
of nutrients in the blood
would vary considerably. The nutrients in the blood are kept
constant to a large extent by the activity of the liver. The

The passageway between the left auricle and
left ventricle is guarded by a mitral, two-cupped valve.
The passageway between the left ventricle and the
aorta is also guarded by a valve. By their action,
valves allow the blood to flow in only one direction.

FUNCTIONS OF THE LIVER

161

stomach, small intestine, spleen, and pancreas receive blood from
the capillaries in those organs and send it to a large vein called the

fish-

amphibian reptile.

mammal.

Among the vertebrates, animals are found with different numbers of chambers in the heart. The
heart of mammals is really two separate hearts, each composed of an auricle and a ventricle.

portal vein. This vein breaks up into capillaries in the liver. By
means of osmosis the liver cells either take out excess nutrients or
give needed sugar to the blood. Another vein, the hepatic vein,
then carries the blood with its normal content of nutrients to
the inferior vena cava. It takes, approximately, thirty seconds
for the blood to make a complete circulation. -

Functions of the liver. The liver, like all other organs, con-
sists of cells. These cells use oxygen and food and give up carbon
dioxide, water, and urea. The partially disintegrated red cor-
puscles are completely destroyed in the liver. The liver uses some
of these corpuscles and other substances as a basis for the manufac-
ture of bile. The function of bile was discussed in a former chapter
(page 132). Excess glucose is stored in the liver in the form
of glycogen or animal starch. When the cells of the body need
sugar, this glycogen is ^converted back into glucose and absorbed
again by the blood. Protein is not stored in animal cells ; there-
fore, excess proteins must be destroyed. This destruction is ac-
complished mainly by the liver. The carbon, hydrogen, and oxygen
are taken from the protein or amino-acid and stored as glycogen.
Through an oxidation process, urea is formed in the cells from the
nitrogen, sulphates from sulphur, and phosphates from phosphorus.
These are given into the blood and are extracted by the kidneys.

162

CIRCULATORY SYSTEM
SPECIAL FUNCTIONS OF BLOOD

Blood Givks

Blood Takes

Skin . . .

Water, organic salts, urea, excess
heat

Lungs . . .

Carbon dioxide, water

Oxygen

Kidneys . .

Water, urea

Small

Materials for making digestive

Secretin, digested nutri-

intestine .

juices

ents, water

Liver . . .

Excess protein, excess sugar,

Needed sugar, urea, excess

secretin, worn-out red cor-

sugar, and organic sub-

puscles, materials for manu-

stances

facture of bile

Blood functions. As the blood circulates through the various
organs of the body, it gives up certain materials and takes in others.
Those functions that take place in all cells are called general func-
tions; those peculiar to any organ are called specific functions.
Assimilation and oxidation are activities performed in all cells;
therefore, they all need food and oxygen and all give up carbon
dioxide, water, and urea to the blood. These are known as
general functions. Since each organ has a special work, there are
certain activities performed by the blood in relation to these
particular functions. In the above table a list is shown of special
work carried on by the blood in some of the organs.

Questions and Suggestions

1. Compare arteries, veins, and capillaries as to (a) position, (b) size,
(c) structure, and (d) function.

2. Explain how to take a pulse.

3. Trace a complete circulation, naming, in order^ all the blood ves-
sels traversed from the time the blood leaves the left ventricle until it
returns.

4. What is the function of each of the systems of circulation : (a) sys-
temic, (6) pulmonary, and (c) portal.

CHAPTER XVII

LYMPHATIC
SYSTEM

Lymph tubes.

Enlarged lymph gland.

How was the circulation of blood first demonstrated f What is the
relation of lymph to blood f What effect has alcohol on the heart f

Historical survey of the circulation. The study of the circu-
lation was one of the first biological investigations that was con-
ducted experimentally. In the early seventeenth century, Galileo,
the Italian physicist, had performed and observed experiments on
falling bodies, and William Gilbert of England had experimented
with electric and magnetic attractions. Due to their work and in-
fluence William Harvey (1578-1657) began to make some experi-
mental investigation in biology. The Greek anatomist, Galen
(131-201 a.d.), had taught that there was an ebb and flow of blood
within both veins and arteries throughout the body. He thought
that the left side of the heart contained blood which was vita-
lized, by a mixture of animal spirits in the lungs. The veins were
supposed to contain crude blood. He believed that the blood
passed from the right to the left side of the heart through very
minute pores in the partition. It was also supposed that one kind
of blood flowed from the liver, to the right ventricle, to the lungs,
and then through the veins, while another kind of blood flowed
from the left ventricle to the lungs and then through the arteries.
In 1510, Leonardo da Vinci wrote a manuscript which included notes
and drawings of the heart and the blood vessels. He had studied

163

164 LYMPHATIC SYSTEM

the movement of the heart in living pigs and he explained how
the aorta led from the heart and branched and ramified through
all parts of the body. Sometime later, Vesalius attacked one of
Galen's beliefs by doubting the existence of pores in the partition
in the center of the heart. But people were still under the influ-
ence of traditional teaching, and would not willingly discard too
much of that which had been previously taught. In his dissec-
tions, Vesalius had noted the parallel arrangement of the arteries
and veins, but he still did not observe that the blood moved in a
circuit. Another investigator, Cesalpino, in 1571, ventured the
opinion that some of the blood left the heart through arteries and
returned by, the veins. He seems to have reasoned this out with-
out experimentation. In 1616, Harvey stated that he not only
failed to find pores in the heart through which blood passed
from one side to the other, but that the partition of the heart
was unusually solid and compact. He examined the heart
action of some forty different animals and described the pulsa-
tions. He examined the circulatory system of a dead man
by making an injection of warm water from the pulmonary
artery through the lungs into the left ventricle. He finally
concluded as a result of his observations and experimentations
that the blood moves in a circuit, and that the beating of the
heart supplies the propelling force. Although he understood that
the blood moved in a " kind of circle," he did not know about the
capillary network connecting the arteries and veins. Malpighi, in
1660, was the first to observe, with the aid of lenses, that the blood
moved through the capillaries from the arteries to the veins.

Harvey's work was the result of reasoning based on the obser-
vations of the structure and pulsations of the heart. He explained
how the contraction of the heart forced blood into the arteries and
how this movement produced the pulse. He pointed out that
the amount of blood which left the left ventricle of the heart in a
given time must return and be sent out again, because, in a half

SOURCE OF TISSUE FLUID

165

hour or less, the heart, by successive pulsations, forces into the
aorta more blood than that found in the entire body. Harvey's
discovery of the circulation of the blood opened up the field of
physiology for later investigators.

Source of tissue fluid. The liquid from the blood plasma is
continuously being diffused through the walls of the blood vessels,
into the tissue spaces where it is known as tissue fluid. This fluid
differs from blood in that it lacks red corpuscles and may have a
higher content of waste materials due to
the collection of wastes from the cells.
White corpuscles can make their way
through the cells in the walls of the capil-
laries and escape into the tissues; there-
fore, they may be found in tissue fluid.

Lymph vessels. Special vessels, similar
to capillaries and veins, drain the excess
fluid as it collects in the tissues, and return
it to the blood. These are called lymph
vessels or lymphatics and the fluid in them
is now called lymph. The fluid that col-
lects in a blister is lymph or tissue fluid.
Even the smallest lymphatics are closed off
from the tissue spaces by very thin mem-
branes. These minute vessels lead to ves-
sels of increasing size until they finally
unite into two very large ones above the
heart. The one on the left, called the
thoracic duct, carries the lymph flow from
the left side of the head and chest, also
from the left arm, abdomen, and the two
legs. The one on the right drains the lymph from the right
side of the head and chest, and the right arm. They both lead
into the venous system from an outlet in the superior vena cava

Lymph vessels, known as
lymphatics, drain the fluid
from all the tissues of the
body. Ultimately, they lead
into a vein of the blood system.

166

LYMPHATIC SYSTEM

near the heart. Valves similar to those found in the veins are

along the larger lymphatics and prevent the back flow of the lymph.

In addition to the lymphatics that drain the tissue fluid, there are

,%**"• ~ some called lacteals

El-

plccsmcc

Liquid materials soak through the walls of capillaries and
bathe the tissue cells. Spaces among the cells are called
lymph spaces. The excess lymph is gathered up by special
tubes, lymph tubes. A lymph tube is shown in the diagram
to be parallel to a blood vessel (this representation is dia-
grammatic).

that are in the villi of
the small intestine.
These lymphatics aid
in the absorption of di-
gested nutrients, par-
ticularly fats. After
a meal, the lacteals
are filled with a white
fatty substance. At
other times, the fluid
filling the lacteals is
very similar to the
lymph in the other
lymphatics. Lymph
is kept moving by the contraction of skeletal muscles squeezing
the lymphatics. This is similar to the effect of the skeletal
muscles on the veins. The flow of lymph is also controlled by the
muscular movements of the body, and by the release of pressure
on the thoracic duct during each inspiration. This release causes
the lymph in vessels where the pressure is greater, to flow into the
thoracic duct.

The spaces formed between the membranes and the various
organs of the body which they cover are similar in structure to
lymphatics, and may be thought of as expanded lymph spaces.
The fluid found in the pleural, the pericardial, and the peritoneal
sacs is similar to the lymph in the lymphatics.

Lymph nodes are expanded portions of the lymphatics found
in all parts of the body. Large collections of them are located
under the arms and in the neck. Others, in fewer numbers, occur

HYGIENE OF THE CIRCULATORY SYSTEM 1G7

in many other parts of the body. They are made of fibrous
tissues interspersed with numerous spaces. In these spaces, white
corpuscles collect and multiply by division. Bacteria are frequently
brought to the lymph nodes, where they are destroyed by the pha-
gocytes, germ-killing white corpuscles, which are found in such num-
bers in the lymph nodes that they have little difficulty in destroy-
ing bacteria. Occasionally, bacteria escape from the nodes and
travel through the lymph into the blood and thus spread infections.
If bacteria multiply rapidly and cause an infection in a lymph
gland, a wall of calcium is sometimes deposited around the germs.
This prevents the bacteria from escaping into the system. A
gland of this kind can be cut out and thus the infection is re-
moved. A lymph gland acts as a sieve to remove bacterial and
foreign materials and thus prevents many injurious substances from
getting into the blood and returning to the heart. The lymph
glands of miners frequently become clogged with dirt and, there-
fore, become greatly enlarged.

Hygiene of the circulatory system. Blood vessels are kept in
tone and the blood is kept circulating normally by regular exercise,
fresh air, good food, hot and cold baths, and sufficient sleep. A large
part of the repair of the body takes place during sleep. Many red
corpuscles are made at this time. If one does not get enough sleep,
pallor may result, which is due to an insufficient number of red cor-
puscles. This may cause anaemia. Regular exercise is better than
spasmodic exercise. When a person does not exercise sufficiently,
the heart and arterial muscles become weak and the muscles all
through the body lose their tone. Any unusual exercise will then
cause palpitation of the heart. Violent emotions overstimulate the
heart and blood vessels. Occasionally, this causes the rupture
of a blood vessel. A violent fit of anger has been known to cause
a condition of this kind. Drinking water is invaluable in aiding
the blood to give off waste materials collected from the cells, into
the organs of excretion ; namely, the lungs, skin, and kidneys.

168 LYMPHATIC SYSTEM

The cells of the body depend upon the circulatory system for
the distribution of building and fuel materials. The importance
of the circulatory system is, therefore, apparent. If violent physi-
cal exercise takes place shortly after a meal, a greater supply of
blood is sent to the working muscles and withdrawn from the di-
gestive organs where energy is needed. Indigestion may result.

When blood congests in veins, it causes the veins to become en-
larged and these vessels are known as varicose veins. This con-
dition frequently occurs in people who do not exercise or have to
stand for long periods of time. Tight garters will retard the cir-
culation of the blood and cause congestion. The arteries of many
elderly people lose their elasticity. This may be caused by too
much physical work, too much mental work, or by poor digestion.
Calcium salts may accumulate in the walls and cause them to
harden. This condition is known as hardening of the arteries, or
arteriosclerosis.

When capillaries are broken, but the skin is unbroken, the injury
is a bruise. Alternate hot and cold applications will usually have a
stimulating effect. When the skin as well as the capillaries are
broken, the injury is an abrasion. It should be washed with an
antiseptic and bandaged to prevent infection. If arteries are cut,
the blood flows in spurts ; pressure must be applied between the
cut and the heart in order to prevent loss of blood. This pressure
is best applied by means of a tourniquet which should be released
every few minutes in order to keep the blood circulating in the limb.
Stopping the flow of blood will help to clot the blood. If a vein
is cut, the blood flows smoothly. In this case, the tourniquet
should be applied on the side of the cut away from the heart.
These are first-aid measures only, and in case of an injury to a vein
or artery of considerable size, a physician should be called to treat
the cut.

Alcohol is believed to injure the white corpuscles to such an ex-
tent that they lose their ability to destroy germs. It also dilates

HYGIENE OF THE CIRCULATORY SYSTEM 169

blood vessels, causing them to lose their ability of contracting and
relaxing. Tobacco is likely to cause palpitation of the heart.
Both alcohol and tobacco seemingly interfere with good physique.
For that reason, part of an athlete's training is abstinence from
them. Good health habits exclude alcohol, tobacco, and drugs.

Questions and Suggestions

1. How was it possible for early scientists to study the circulatory
system scientifically ?

2. What three erroneous ideas in regard to circulation were ex-
ploded through the scientific method ?

3. Draw a diagram of a liver cell, a lymphatic, and a capillary. By
means of labeled arrows, indicate the possible exchanges of materials.

4. In what cells in the body can blood leave an unusual supply of
(a) calcium, (6) fat, (c) worn-out red corpuscles, (d) protein for destruc-
tion ? Where can it collect (a) oxygen, (6) urea, (c) white corpuscles,
(d) glucose?

5. What is the relation of the lymph system to the blood system ?

6. What rules of health should be followed if the organs of circu-
lation are to be kept in the best possible condition ?

7. In terms of circulation, discuss a possible cause of each of the
following diseases : anaemia, varicose veins, and hardening of the
arteries.

Supplementary Readings

Haggard, H. W., The Science of Health and Disease (Harper & Bros.).
Kimber, D. C, and Gray, C. E. Textbook of Anatomy and Physiology (The
Macmillan Co.).

WH. FITZ. AD. BIO. — 12

1 *• • . y

• '.i

(6 !St

CHAPTER XVIII

THE SKIN

AND
KIDNEYS

Excretory organ of Parame-
cium.

Excretory organ of earth-
worm.

What is the necessity for excretion f How are wastes eliminated from
the body f What is the relation of the skin and kidneys to excretion f

Importance of excretion. The wastes formed in the various
tissues as a result of oxidation are carbon dioxide, water, organic
salts, and urea (nitrogenous compound) . These wastes would in-
terfere with the normal functions of the cells unless removed as
quickly as formed. The removal of these wastes is called excre-
tion, and the organs that eliminate the wastes are called the excre-
tory organs. The importance of an efficient system of elimination
can not be sufficiently emphasized. Carbon dioxide is eliminated
chiefly by the lungs, although some is dissolved in water and
is excreted by the skin and kidneys. Water and some soluble
salts are eliminated by the skin as perspiration, and by the kid-
neys as urine. Some water, however, passes out of the lungs in
the form of vapor. Most of the urea is excreted through the
kidneys as part of the urine, and a small amount through the skin
x as part of the perspiration.

Problem. Study of the skin.

I. Touch the skin and describe how it feels.

A. Explain the source of the heat in the skin.

B. When one is exercising violently, why does the skin become much
warmer than it does at other times ?

170

STUDY OF THE SKIN 171

II. Describe the skin of the hand as it appears to the eye. Tiny structures
in the deeper layers of the skin push up the outer layer into little ridges.

A. Note the arrangement of the lines on the tips of the fingers, particu-
larly the thumb. Describe the arrangement.

B. Moisten the finger slightly and, if convenient, touch powdered car-
bon with it. Then press it on clean blank paper.

1. What is the impression called?

2. What use may finger prints serve ?

C. Examine your skin and observe whether it normally has breaks or
abrasions on it. What is the value of an unbroken skin ?

III. Hold the hand out straight and then clinch the fist. Does the skin
appear dry and brittle or soft and flexible ?

A. This characteristic is due to oil secreted in oil glands in the skin.-

B. Describe what may have happened to cause dry skin.

'IV. Touch your tongue to the back of your hand. Describe the taste.
This is due to perspiration secreted by sweat glands in the skin.

A. Why is the perspiration not always seen on the skin?

B. What condition favors the evaporation of the perspiration ?

C. What condition hinders the evaporation of the perspiration ?

D. Under what conditions do we perspire excessively ? Why ?

V. If wet-and-dry-bulb thermometers are available, pour a little water on
the bulb.

A. After a few minutes, read and record the temperature of each
thermometer.

B. What effect has the evaporation of moisture on temperature?

C. What effect would you expect the evaporation of perspiration to
have on the temperature of the body ?

VI. Hold the hand so that the back of it is on a level with the eyes. Note
the hairs covering it. These hairs probably help to absorb perspiration from
the skin.

VII. Cite some evidences of the skin gradually peeling from your body.
This is the outer dead skin called the epidermis.

VIII. Prick the skin gently with a pin. As a result of the pin prick tell :

A. What two sensations may be experienced by the nerve endings in
the skin.

B. What other sensation may be experienced by skin ?

IX. Summarize your answers to the above questions by stating four
functions of skin.

172

THE SKIN AND KIDNEYS

por« ofsvteat ^lan^t'&uer^

opi2lerm.iV

Structure of the skin. The skin is a smooth, moist, flexible
organ varying from one one hundredth to' one tenth of an inch in

thickness. It consists
of an outer layer called
the epidermis, and an
inner layer called the
dermis. As the cells
grow out in the deep-
est part of the epider-
mis layer, they are
gradually transformed
into flat scales. The
outermost layers are
dead and are being
constantly rubbed off
the surface of the skin.
The deepest layer of
the epidermis contains
pigment cells, and is
called the Malpighian
layer after the scien-
tist who first observed
it. There are normal pigments in this layer, which are the basis
for white, yellow, red, or black skin colors of various people. In this
layer may develop deposits of pigment, which are known as freckles.
The dermis is the true skin. It is composed largely of connec-
tive tissue. Tiny muscles may run through the dermis. These,
by contracting, will cause the tiny hairs in the epidermis to stand
erect. They also cause the " goose flesh " when a person is cold.
The contraction of millions of tiny muscles give a little heat and,
at the same time, a warning that the body is cold. . The dermis is
richly supplied with blood vessels, lymph vessels, nerves, and hair
follicles. The blood vessels carry water in which urea and carbon

nG>rve

The surface cells of the skin are constantly wearing or
washing off and are replaced by cells underneath. Blood
vessels nourish the skin; and the various nerve endings re-
ceive different stimuli from the environment.

STRUCTURE OF THE SKIN

173

dioxide are dissolved. Some of the wastes are eliminated by
sweat glands. Each sweat gland ends in an opening in the epi-
dermis called a pore. The perspiration leaves the body through
the pores. . Specialized epithelial cells form roots of hairs in the
deeper layers of the true skin. These hairs grow out through
hair follicles which are formed by the downward extension of the
epidermis. Only the lower part of the hair lives and grows.
Associated with the hair follicle is an oil gland. This supplies
nourishment to the hair since it opens either into a hair follicle
or upon the surface of the skin. The oil keeps the skin flexible
and soft. Within the tiny papillae or end-organs in the dermis
are specialized nerves for receiving the sensations of pressure,
pain, and temperature. Fat cells are also found in the dermis.

Functions of the skin. The skin is an organ of excretion. By
means of the millions of blood vessels, sweat glands, and pores, it

Hairs grow from hair follicles formed by
the downward extension of the epidermis
into the true skin. The hair in the bottom of
the follicle enlarges to form a bulb which is
well supplied with blood vessels.

<K>W..J ■■■

A sweat gland is composed of a duct and
a coiled portion surrounded by capillaries.
Wastes gathered from the blood by the
glands are eliminated through a pore in the
skin.

174

THE SKIN AND KIDNEYS

•proeevtre—

The ski a is an organ of feeling. The
papillae put us in touch with our environ-
ment by sensing pressure, pain, and tem-
perature.

excretes on an average of a quart of perspiration daily. In cases
of kidney trouble, it may relieve the kidneys by secreting more
wastes. The skin is an organ of protection. By means of its un-
broken outer dead layer of epi-
dermis, it protects the underlying
living dermis from an excessive
loss of water and from the in-
vasion of germs and dirt. The
skin is an organ of sensation.
By means of the papillae in the
dermis, it receives sensations of
pressure, pain, and temperature.
The skin is invaluable in equaliz-
ing and maintaining the proper
body temperature. If the body is too warm, a greater supply of
blood is sent to the skin so that the heat will radiate. If the body
is not sufficiently warm, the blood vessels in the skin contract and
very little heat radiates out. The evaporation of the perspira-
tion on the skin cools the body.

Hygiene of the skin. When the water of the perspiration evap-
orates, organic salts and urea clog the pores. These wastes can best
be removed by warm, soapy baths. If left in
the pores, the wastes, resulting from perspira-
tion, give the body an objectionable odor. A
tepid bath should be taken at least twice a
week. Cold showers are stimulating to the skin,
muscles, and the blood vessels, and, if possible,
should be taken daily. Dirt may clog the
pores in the skin and cause blackheads. If the
skin is kept clean, blackheads will not form.
Sometimes bacteria clog the pores, and cause infections, pimples,
or possibly boils. Pimples should not be pinched or scratched
with the fingers as bruises may result and cause more serious

taste

Papillae on the tongue
contain nerve endings
which transmit taste
stimuli to the brain.

THE KIDNEYS

175

infections. Let them heal naturally or have a physician care
for them. When pimples become chronic, the condition is
called acne. If acne is

kidney;
ccortcc
vena cava

wreter*

blaaaer

The kidneys gather liquid wastes from the blood.
These materials are passed through the ureters to the
bladder and held in this reservoir ready for excretion.

treated in time, it can
be cleared up completely.
If not, it leaves scars
that are permanent.
Any unhygienic condition
of the body is likely to
affect the skin. In order
to keep the skin in good
condition, hygienic sug-
gestions concerning food,
water, rest, exercise, and
sunlight should be fol-
lowed.

The kidneys. The or-
gans that excrete most of
the water and urea from the body are the kidneys. They lie in
the abdominal cavity in the small of the back above the waist
line. They are bean-shaped with the concave side turned toward
the spine. The bulk of the kidney is made up of small coiled

tubes, tubules, closely packed
together and containing a large
number of blood vessels, and
some nerves and lymphatics.
Water, urea, and organic salts
pass by means of osmosis into
the tubules. These tubules
lead into two tubes, one
from either kidney, the ureters, which are connected to a hollow
muscular sac called the bladder. The kidneys secrete urine which
passes down the ureters to the bladder. The bladder serves as a

mn-mm

ttfbule of

The kidneys are made up of numerous minute
tubules. Their intimate relation with blood ves-
sels makes possible the absorption of wastes.

176 THE SKIN AND KIDNEYS

reservoir for the urine until it is expelled from the body. When
the bladder is moderately distended, it holds about one pint. The
average quantity of urine secreted in twenty-four hours by the
average adult is about forty ounces, or 1.2 liters. The kidneys
eliminate toxic materials formed in the body during illness. In
ridding the body of its poisons, the kidneys are frequently dam-
aged. In order to keep them in as good condition as possible,
about seven glasses of water should be drunk daily. This will
dilute any toxic materials present and keep the kidneys well
washed. Too much animal protein food should not be eaten as
the kidneys may become overworked, in eliminating the urea, an
oxidation product of proteins.

Questions and Suggestions

1. What is excretion?

2. Name the organs of excretion and discuss how each one elimi-
nates waste.

3. Name four functions of the skin and explain the ways in which
the skin is adapted to perform each function.

4. Discuss the hygiene of the skin.

5. What unhygienic habits may injure the skin ?

6. What is the relation of the work of the skin to the work of the
kidneys ?

7. Discuss the value of water to the skin and kidneys.

Supplementary Reading

Kimber, D. C, and Gray, C. E., Textbook. of Anatomy and Physiology (The
Macmillan Co.).

CHAPTER XIX
RESPIRATION

Tracheae of insects.

Gills of fish.

What is the relation of respiration to excretion f
perform their function?

How do the lungs

Most of the carbon dioxide and some of the water, formed by
the body cells during the oxidation of food materials, are eliminated
through the lungs. There are no organs in a higher plant similar
to the lungs of man, although the stomata, openings for the in-
take and outgo of air, in leaves are concerned with the function
of respiration in the plants. The abundance of these stomata
make up for their microscopic size. ,They are found in the epi-
dermal tissues of a leaf and they lead to air spaces among cells
between the two layers of epidermis. These openings are not
adapted for securing large quantities of air at one time. They
may be compared to the nostrils of man rather than to the lungs.

Lower animals have various devices for securing air. An insect
has small openings in the abdomen and thorax which lead into
branching tubes. These tubes subdivide until they can reach the
smallest cell in the body. By compressing and releasing their
body regions, somewhat like a bellows, the animals are able to
take in oxygen and give out carbon dioxide. Watch the abdomen
of a fly or a bee and note the breathing movements. A fish has
gills which are branched structures with such thin walls that air
can pass directly from the water into the blood stream. The air

177

178

RESPIRATION

is taken from the water which is drawn into the mouth and forced
out through the gills. Respiration takes place in every living cell,
but breathing is only possible in the higher animals that have lungs.
The air tubes. The outer openings of the air tubes of man are
the nostrils. These lead into two nasal passages terminating in the
throat cavity. The nasal passages are specially adapted for pre-

ctiaphrdc^txLli

The breathing organs of man are arranged in a continuous passageway from the nostrils
to the ends of the bronchial tubes. These tubes subdivide and terminate in air sacs.

paring air for the use of the body. The hairs in the nose act as a
filter, to keep dust and other foreign particles from entering the
lungs. The mucous lining absorbs the fine foreign particles and
inhibits the development of germs. The mucous lining also
moistens the air. Very dry air is irritating to the lungs.

The air is warmed in the nasal passages by coming in contact
with the blood vessels in the linings of the narrow passageways.
Air then passes through the glottis into the larynx or voice box.

THE LUNGS 179

The larynx contains some thickened cartilage, popularly called
Adam's apple, which projects slightly on the front of the neck. The
air passes down the trachea or windpipe into the two branches,
the bronchi, which subdivide again and again into the bronchial
tubes, which in turn end in small pouchlike sacs called the air
sacs. All of the air tubes are lined with mucous membrane
vvhich warms and moistens the air. The trachea is lined with
specialized epithelial cells bearing hairlike processes or cilia. These
cilia are in constant motion. Their function is to push or move any
solid particles, in the air, into the throat, where they are expelled.

There are numerous capillaries in the air sacs. The walls of
the capillaries are membranous and air easily diffuses through
them into the blood. The red corpuscles take the oxygen from
the air. Thus blood becomes oxygenated. At the same time, the
blood gives out its carbon dioxide. The air sacs may be com-
pared with tiny balloons. The fact that they are so numerous and
are capable of such inflation affords a tremendous surface for the
absorption of oxygen even though the lungs themselves are fairly
small. The large absorbing surface of the air sacs makes possible
the presence of a tremendous number of capillaries running through
them. Therefore, a great deal of oxygen quickly passes into the
blood and carbon dioxide passes out. The lungs consist of mil-
lions of air sacs and bronchial tubes held together by connective
tissue. The moist membranous pleurae cover the lungs, and pre-
vent friction during the breathing movements.

Diseases of the respiratory tract. The mucous membrane
lining the pharynx contains many lymph glands and at the back
and upper part of the cavity there is a large mass of this lym-
phoid tissue. During infancy and childhood this tissue may
increase greatly, and the child is then said to have adenoids.
Adenoids are a menace to health. They may obstruct the openings
to the Eustachian tubes, and in some cases cause deafness. - They
usually interfere with the passage of air through the nose and

180

RESPIRATION

occl«noicL

necessitate mouth breathing. This not only allows dust and other
foreign particles to pass into the lungs, but tends to alter the shape
of the jaws and facial features. Malformations of teeth are fre-
quently caused by adenoids.
Mouth breathing is usually
a forced breathing and
frequently alters the shape
of the chest.

In the lower part of the

Thickened mucous membranes may form abnormal throat, On either side, are

growths, known as adenoids, in the back of the nasal .. » , l • j

passageways. Tonsils are the normal growth of lym- Small masses 01 lymphoid

phoid tissue in the throat. ,. „ i /nW/» The

LlooUC CdllCLl LUILol/Vo. .JLJlv

function of the tonsils is not understood exactly. They are
thought, when in a normal condition, to help protect the body
from infection by acting as filters and preventing the entrance
of bacteria. If they become infected with bacterial growths, they
serve only as centers of infection. When they are infected, the
pus in them passes directly into the lymph and then into the blood.
This may cause such conditions as rheumatism, anaemia, or pro-
duce an undesirable heart condition. If the tonsils become much
enlarged, they fill the throat cavity and interfere with the passage
of air to the lungs and of food to the gullet. Inflammation of the
tonsils is called tonsillitis.

Problem. Study of the lungs.

Secure the lungs and windpipe of a sheep or lamb from the butcher.

I. Try to cut the windpipe or trachea.

A. Describe the structure.

B. What is the value of the presence of cartilage in the trachea?

C. Describe the arrangement of the cartilage in the trachea.

II. Observe the appearance of the lungs.

A. Describe the outer shiny covering. Discuss the functions of the
covering.

B. Describe the structure of the lungs, including the shape, texture,
color, and tissues present.

MECHANISM OF BREATHING 181

C. Insert a glass tube in the trachea and breathe into it.

1. What effect has this on the lungs?

2. When you blow into the lungs, do you find any structuresjthat
might account for the texture of the lungs ?

III. Cut out a small piece of the lung tissue where the bronchus enters it.

A. Describe the branches of the bronchus in the lungs.

B. Try to trace one of the tubes until it ends. How does it end ?

Problem. Study of the mechanics of breathing.

Place a cork, through which runs a glass rod, in the mouth of a small-sized
bell jar. Attach a balloon to the end of the rod inside the jar. Cover the
bottom of the jar with a piece of rubber sheeting in the center of which a string
is attached.

I. To what structures in our bodies are the glass tube, balloon, bell
jar, and rubber sheeting comparable ?

II. Pull the string gently, so that the rubber sheeting moves down.

A. What effect has the lowering of the rubber sheeting on the balloon ?

B. Is the balloon pressed on by air in this position of the rubber sheet-
ing as much as in the former position ?

C. When the pressure on the outside of the balloon is released, what
effect has it on the air in the balloon ?

D. Why, then, does air enter the balloon ?

E. To what is this comparable in human breathing ?

III. Push the rubber sheeting into the battery jar to form an arch.

A. What effect has the arching of the rubber sheeting on the balloon ?

B. In this position, is the balloon pressed on by air as much as in the
lowered position ?

C. When the pressure on the outside of the balloon is increased, what
effect has it on the air in the balloon ?

D. Why, then, does air go out of the balloon ?

E. To what is this comparable in human breathing ?

IV. To what is the inflation and deflation of air in the balloon due ?

V. What is one of the reasons for inspiration and expiration in man ?

Mechanism of breathing. Air with its oxygen is taken in, and
air with increased amounts of carbon dioxide is given off as a re-
sult of muscular activity. The floor of the chest cavity is formed
by the muscular diaphragm. The upper surface of the diaphragm

182 RESPIRATION

is arched around the lower part of the heart and lungs. When
its muscular portion contracts, the diaphragm flattens and moves
downward, while the ribs are elevated. The spaces between the
ribs are filled by muscles. When these muscles relax the ribs
return to their original position. This reduces the chest cavity
from side to side. The diaphragm now returns to its original
position and the abdominal walls contract and push the liver and
stomach against the diaphragm, which contracts, presses against
the lungs, and in so doing, pushes out the walls of the chest
cavity, front and back. Thus the chest cavity is increased in size
from top to bottom by the contraction of the diaphragm, and
from back to front and side to side by the activity of the muscles
between the ribs.

The lungs are as large as the cavity they occupy. When the
chest cavity increases in size, the lungs are no longer pressed
upon, and, since they are somewhat elastic, they fill the space
made by the expanding chest. The air in the lungs now spreads
out to fill the space formed by the enlarging of the lungs. Move-
ment of air always occurs when there are differences in pressure.
As the air spreads out, its density becomes lower. Air rushes in
from the outside to equalize the pressure. This is inspiration or
the taking in of air. The blood vessels in the air sacs are thus sup-
plied with air from which the haemoglobin extracts oxygen and
to which it gives up carbon dioxide.

Expiration is the forcing out of air. It is due to the relaxation
of muscles which crowd the lungs into a smaller space. Air in the
lungs is then denser than air outside and it is expelled in order to
equalize the pressure. This is expiration. The taking in of the
air, the exchange of gases in the air sacs, and the giving out of air
is breathing or respiration.

Cell respiration.* When the oxygen of the air gets into the blood,
it is carried to the cells. It passes from the blood through the
walls of the capillaries, through the lymph spaces and into the cells.

THE RATE OF RESPIRATION 183

Oxidation of the food then takes place, releasing energy for cell
work and forming the wastes, carbon dioxide, water, and urea.
The carbon dioxide is given off to the blood. Respiration is of
two types, external respiration and internal respiration. External
respiration is concerned with inspiration and expiration. Internal
respiration involves the exchange of air between the blood and
tissues.

The rate of respiration. The average rate of respiration for an
adult is twelve to sixteen per minute. This rate is partly deter-
mined by the amount of carbon dioxide in blood. If this amount
rises above a certain percentage, the nerve centers controlling res-
piration are stimulated and this results in deeper breathing at an
increased rate. Thus more oxygen is obtained and the carbon
dioxide is removed more rapidly. This explains the second wind
of athletes. Due to violent exercise, a great deal of oxidation
takes place, causing the accumulation of carbon dioxide in the
blood. Then the nervous response follows, increasing the respira-
tory rate and giving the athlete more oxygen for releasing more
energy. The rate of respiration may, also, be influenced by strong
emotion and by old age. In respiration, the lungs are never
emptied of air; only about one tenth of the air is normally
changed with each respiratory movement. This is called tidal air.

Problem. Modifications of breathing.

I. Analyze the type of respiration, and next to each write whether it is
an inspiration or an expiration in each of the following : yawning, sighing,
sneezing, coughing, hiccuping, sobbing.

II. Explain how the control of the diaphragm will probably suppress any
one of them.

The air we breathe. Inspired air contains about 20.96 per cent
oxygen, 79 per cent nitrogen, and 0.04 per cent carbon dioxide:
Expired air contains about 16.4 per cent oxygen, 79 per cent ni-
trogen, and 4.1 per cent carbon dioxide. The same air can be
breathed many times before the oxygen is entirely exhausted.

184

RESPIRATION

Through experimentation, scientists have discovered that people
are most uncomfortable in still air. Under the clothing, in close
contact with the skin, is a blanket of air. This air absorbs per-
spiration, body odors, and the excess body heat. If this air can-
not circulate, it becomes moist, and the perspiration does not
evaporate as it should. If air in a room is set in motion by an
electric fan, the contaminated and moist air moves, and cooler
and drier air takes its place. This brings relief to the body. For
years, people thought ventilation consisted largely of getting rid

from, Tieart
to tissue cells

Ctno.u* Sac
of -tftc. lung

incoming ovr tdiili ojp*£«^
ou*co*ntW*o«V* owWLIess

The exchange of carbon dioxide and oxygen between the air sacs and blood vessels is external
respiration ; between the cells and blood vessels it is known as internal respiration.

of carbon dioxide. Now it is known that ventilation problems
also involve the control of body odors, heat, and moisture.

When air is set in motion, the stagnant air is removed and
fresh air is brought in contact with the body. Air that is best
for breathing should be at a temperature from about 65 degrees
to 70 degrees. It. must be slightly moist, must be moving, and
must be free from dust and impurities. The problem of venti-
lation is to treat the atmosphere of a room so that air will have
at all times the four characteristics mentioned.

METHODS OF VENTILATION 185

Methods of ventilation. Many systems of ventilation have been
devised, but probably in many places none works as efficiently as
properly regulated windows. Windows should be opened at the
top and bottom during both day and night. Air comes in the
lower opening, becomes heated, rises, and goes out through the
upper openings. Care should be taken that drafts are kept out
of the room since these are likely to chill the body. A board
placed at the bottom of an open window can be arranged so as to
drive the air upward and will thus prevent drafts. In winter,
care must be taken to keep the air moist. If the air is too dry,
the mucous membrane lining of the nose and throat will become
dry and irritated, probably resulting in inflammation in the res-
piratory tract. The various methods of heating homes are likely
to dry the air. The evaporation of water in pans placed under
or on radiators will aid greatly in moistening the air. To-day,
we find that ventilating systems are included in many of the
modern heating plants. In these systems the same air is circu-
lated repeatedly. It is washed, heated or cooled, and freed of
moisture in each circuit.

Hygiene of respiration. A great many deaths are caused an-
nually by diseases of the respiratory tract. Many of these could
be prevented if the respiratory tract were kept in good condition.
The nose is adapted for preparing the air for the use of the
body, and, therefore, it should be used for breathing. Any inter-
ference with nasal breathing should be corrected.

Questions and Suggestions

1. Suggest two experiments that may be used to show that oxida-
tion takes place in the body.

2. Name the adaptations of the respiratory system for (a) puri-
fying air, (6) warming air, (c) moistening air.

3. Make a labeled diagram of the air passages. Trace the path
of air from the time it first enters the body until it reaches the
cells.

WH. FITZ. AD. BIO. — 13

186 RESPIRATION

4. Discuss the mechanics of breathing.

5. State the aims of ventilation.

6. How would you ventilate a room ?

7. What causes discomfort in a poorly ventilated room ?

8. In a diagram containing a cell, lymph space, and a capillary
indicate, by means of arrows, how respiration takes place.

9. Build a box to illustrate a room with two windows. Manipu-
late the windows to illustrate proper ventilation. Candles may be
used to show the best methods of ventilation.

Supplementary Readings

Howell,. W. H., Textbook of Physiology (W. B. Saunders Co.).
Williams, S. F., Healthful Living (The Macmillan Co.).

CHAPTER XX
METABOLISM

Exercise promotes

good metabolism.

What is metabolism? How are the food nutrients used in the body?

Metabolism is the term usually applied to all the processes which
are concerned in the building up and breaking down of the proto-
plasm in an organism. In short, it is the sum total of all the physi-
cal and chemical changes by which the protoplasm utilizes food,
releases .energy, and eliminates waste products in order to maintain,
repair, and produce more protoplasm. The processes of absorp-
tion, assimilation, respiration, and excretion are phases of metab-
olism, while digestion may be called a secondary process which
makes possible the primary activity of absorption. If the process
of metabolism is that of synthesis or building up, it is called an-
abolism, but if the process is one of tearing down, it is katabolism.
When the building up of protoplasm is greater than the breaking
down, growth takes place.

No one function of the body can be discussed without referring
to one or all of the others because many of the functions take place
at the same time. During the anabolic process of assimilation, the
katabolic process of oxidation is also being carried on in order to
release enough energy for the assimilation and growth processes.
Before oxidation is possible, the digestion of the food must take
place. In fact, the process of metabolism involves all the physi-
ological functions of the body as well as the special activities that

187

188

METABOLISM

take place within the cells themselves. No matter what kind
of food is taken into the body, it must first be broken down
into a soluble form, and assimilated by the cell, before it can
be converted into the kind of tissue needed.

Metabolism of carbohydrates. All carbohydrates are reduced
to simple sugars, glucose or galactose, in the digestive process,
by means of enzymes. They are then absorbed by the capillaries
in the villi and sent to the liver by way of the portal vein. The
excess sugar is taken in by the liver and stored there as an in-
soluble form of carbohydrate, known as glycogen or animal starch.
Muscle cells, too, store up small quantities of sugars in the form
of glycogen. This glycogen is then con-
verted, as it is needed, into glucose and
given to the blood. Thus the percentage
of sugar in the blood is kept constant at
0.07 to 0.15 per cent. If more carbohy-
drates are eaten than can be used or stored,
the surplus tends to be converted into body
fat. As the sugar circulates, it is absorbed
in the tissue fluid and cells by means of
osmosis. Here it is oxidized to release
energy in the form of muscular work or heat
to keep the temperature of the body con-
stant. In the oxidation process, sugar is
converted into carbon dioxide and water.
These wastes are carried by the blood to
the lungs, skin, and kidneys for elimination
from the body.

Metabolism of protein. Proteins are de-
composed by enzymes in the digestive tract
into the simple compounds, amino-acids.
These are absorbed into the blood and from there into the tissue
iluid and cells. The body uses the various amino-acids for build-

The food burned in a bomb
calorimeter and the energy
released is carefully deter-
mined. The number of cal-
ories shown in the food tables
is found in this manner.

METABOLISM OF PROTEIN

189

Underwood and Underwood
The amounts of human energy expended in various types of work can be measured by a calor-
imeter. This is done by devices which measure the amount of oxygen absorbed and the amount
of carbon dioxide given off by the subject doing a particular kind of work.

ing new cells and for repairing any wastage. If there is a surplus
of protein materials it is thought that a portion is held as a sort
of storage supply in the liquids or tissues of the body. This sur-
plus is then utilized when the loss of protein from the cell is
greater than the supply needed by the body for repair, as in time
of illness.

If there are more proteins (in the form of amino-acids) than
the cells can utilize, some of the excess is eliminated by the
kidneys, while others are taken care of by cells in the liver.
These cells in the liver are capable of separating the amino-acids
into ammonia and non-nitrogenous products (oxygen, hydrogen,
carbon, sulphur, and phosphorus). The ammonia combines with
other elements to form urea which is eliminated by the kidneys as

190 METABOLISM

fast as it is formed. The sulphur and phosphorus are given off by
the excretory organs, and the carbon, hydrogen, and oxygen com-
bine and are stored in the liver in the form of glycogen. This sub-
stance is then released as the body needs it.

Metabolism of fats. Fats are absorbed as glycerol, fatty acids,
and soaps by the lacteals of the villi. In the absorption process,
they are reassembled as fats, probably by the epithelial cells in the
villi. The absorbed fats travel through the lymphatics to the
thoracic duct which empties them into the venous system just before
draining into the superior vena cava. In this way, they become a
part of the blood. These fats are not in the original form of the
fat ; they are made into a fat which is characteristic of the species
in which the metabolism is taking place. They are carried to the
cells, where they are burned as fuel which serves as a source of
energy for muscular work and other activities. The resulting
wastes, carbon dioxide and water, are eliminated by the organs of
excretion. Some fat is used to build fatty tissue and the extra fat
is then stored in the vacuoles of cells in the form of drops of oil.

Questions

1. Give a definition of metabolism.

2. Classify the functions of the body into anabolic and katabolic
functions.

3. Discuss the metabolism of sugar ; of protein ; of fat.

Supplementary Readings

Burton-Opitz, Textbook of Physiology (W. B. Saunders Co.).
Howell, W. H., Textbook of Physiology (W. B. Saunders Co.).
Martin and Weymouth, Elements of Physiology (Lea & Febiger).
Mitchell, P. H., General Physiology (McGraw-Hill Book Co.).

^Z_voice base

i-tWroicL

i:vin&pipe

ccclrenocL

CHAPTER XXI

DUCTLESS
GLANDS

The. thyroid gland.

An adrenal gland.

' What are ductless glands t How do they affect the development and the
activity of the body? What is the scientific status of gland grafting?

The glands of the body, that have already been discussed, had
ducts to convey their secretions to an outer surface, such as the
mouth, stomach, or skin. Certain glands in the body have no
ducts, but pass their secretions directly into the blood or lymph.
These glands are called endocrine glands (endocrine is from a Greek
word which means " to separate within ") . These glands manu-
facture substances which go into the blood stream, and activate
or influence another organ or organs in the body. These manu-
factured substances are called hormones (from the Greek word
meaning to " excite " or " arouse ").

Internal secretions. The hormone secretin was mentioned
when the digestive system was studied. It is liberated from the
wall of the small intestine when the acid food enters from the
stomach. It is absorbed directly into the blood and is carried to
the pancreas and liver. It stimulates these glands to activity so
that the bile and pancreatic juice immediately start to flow.
Carefully checked experiments have proven that this activity
always takes place. For example, an experiment was given in
the chapter on digestion to show that secretin travels through
the blood from the intestine to the pancreas. Another interest-
ing experiment has been performed to show how digestive juices

191

192

DUCTLESS GLANDS

are produced. Some of the mucous membrane of the small in-
testine was scraped off, treated with acid, and injected into the
~ , blood. Immediately, pan-

creatic juice flowed. The
flow is thought to have
been effected by the stim-
ulation of the digestive
glands by secretin which
was probably formed from
an inactive hormone in the
mucous membrane.

The internal secretions
are of great importance in
bringing about coordina-
tion among the various
organs. It is thought by
some investigators that
every kind of tissue may
give rise to individual sub-
stances or principles which pass directly into the blood, and affect
the general working or metabolism of the body. Not many studies
have been published concerning tissue secretion. To date, in-
vestigations have been confined largely to the hormones of the
ductless glands.

It is difficult to secure the internal glandular secretions of human
beings in a pure state. Therefore, our knowledge concerning
them is based primarily on experimentation >on lower animals,
chemical examination of the glands and their extracts, and of
the blood near the glands, observations of the effects resulting
from disturbances of the ductless glands, and effect of direct
injections of extracted or synthesized internal secretions.

The thyroid. The thyroid is one of the ductless glands. It is
situated in the neck and consists of two divisions or lobes, one on

pineal bo&£
pituitary'

parwthjfn>&s
^~t£g£imcs

.....liver
-pancreas

-a&renals

Most of the ductless glands of man are indicated in
their approximate positions.

THE THYIiOID

193

either side of the voice box or larynx, and usually connected by a
narrow strip of tissue. The entire structure weighs between one
and two ounces. The substance secreted by the thyroid is called
thyroxin and it contains about 65 per cent of iodine. It passes
directly into the blood since there is no duct to convey it from the
gland. Thyroxin influences the rate of oxidation in the body.
The method of testing this rate is by determining the person's basal
metabolism. Basal metabolism means the heat or energy expended
by the body when there is almost complete absence of absorption
from the digestive tract, and almost complete muscular and mental
repose. A normal person who has fasted for fifteen hours preced-
ing the test would use a definite amount of oxygen, depending on
his weight, height, and age. This amount has been determined,
and is a measure of normal basal metabolism. Doctors can tell
whether or not a thyroid gland in any person is overactive by
performing this basal metabolism test. A large amount of thyroid
secretion increases the metabolism in the body, which is noted by
an increase in the amount of oxygen used, as compared with the
amount used by a normal person. A decrease in thyroid secre-
tion results in a lower rate of basal metabolism; that is, less
oxygen is used than that usually required by a normal person.

I Brain...
t"hyroicL _> V y /

pineal £lcttul

■

The location of the ductless glands in the rat.

Thyroids have been removed from animals, and harmful effects
were observed. Other thyroids were grafted in another section

194 DUCTLESS GLANDS

of the body, and the aforementioned results disappeared, although
the effect of the grafted thyroids were only temporary. Extracts
of the thyroid tissue are now given to persons whose glands do
not function properly. In most cases the treatment is successful.

Thyroxin probably has some effect upon growth and develop-
ment of organisms. Gudernatch, while teaching at Columbia
University, has carried on a series of interesting experiments on
glandular feeding. He fed thyroid glands (of different animals)
to very young tadpoles and they promptly went through meta-
morphosis and became frogs. In some cases the frogs were no
larger than a beetle. When he removed the thyroid gland from
other tadpoles, they never became frogs, although they grew larger
than the usual size of a tadpole.

Thyroid deficiency, due to degeneration or an operative removal
of the glands, in an adult gives rise to dullness and general
apathy or sluggishness. The person gets very stout, although his
appetite may be diminished. The heart beats slower, the nervous
system becomes sluggish, and the general intelligence is lowered.
This condition is easily explained by the slow rate of oxidation.
The disease is called myxedema. If in a young child the thyroid
glands waste away, his head and face usually become enlarged, and
look deformed, and his abdomen becomes swollen. The mental
faculties as well as the physical character of these sufferers show
lack of development and often lead to a condition of idiocy. This
disease is called cretinism, and children suffering from it are called
cretins. When thyroid extract is fed to persons suffering from
myxedema or cretinism, they usually improve and sometimes are
completely cured, provided no essential organs have been affected.
This thyroid treatment must, however, be kept up indefinitely
because the patients' glands are atrophied and will remain inactive.^

In some communities, a large percentage of the population shows
an enlargement of the thyroid glands ; -this condition is known as
endemic goiter. It is common in certain sections of our country.

THE THYROID 195

One might think that the thyroid is over active in endemic goiter,
since it is enlarged. However, the reverse is true as the general
symptoms are the same as in myxedema. Thyroid tissue is rich in
iodine. This is a constituent always present in drinking water
of localities near the sea, in sea weed, and in sea foods 'such as
oysters and crabs. When people live in areas remote from the
sea, they drink glacial water which is practically lacking in iodine.
Endemic goiter is usually prevalent in such districts. An example
is our own Great Lake district. Studies have been made in many
schools in these localities. Inorganic iodides have been admin-
istered to the children and iodine has been put in their drinking
water. Within a short time the number of cases of goiter showed
a remarkable decrease. However, it is probably unwise to feed
iodine as a treatment to all people suffering from endemic goiter.
In case the gland is already enlarged, the iodine, may stimulate
the gland to produce too much thyroxin. This would increase
the metabolism of the body. When people suffer from excessive
thyroid activity, foods containing iodine are often removed from
their diets. In all cases iodine should be used only upon the
advice of a physician.

An excessive secretion of thyroxin gives rise to a disease called
exophthalmic goiter. The symptoms'are just the opposite of those
in underactivity of the gland. Instead of a stupid, apathetic con-
dition there is a restless, nervous one. There is a wasting away of
tissues in spite of an enormous increase in food consumption. The
pulse and heart action are very rapid and often irregular. The
thyroid usually increases in size accompanied by an abnormal
protrusion of the eyeballs. There are various treatments, the most
successful being complete rest in order to slow up metabolism.
Sometimes, X-rays are used to check the activity of secretion and
sometimes the gland is partially removed. A more common
operation is the tying off, temporarily, of one of the blood vessels
in order to lessen the amount of the secretion reaching the blood*

196

DUCTLESS GLANDS

The parathyroid. There are four small structures attached to
the thyroid glands, and weighing in all about two grains. They are
the parathyroids (para means "near"). These, also, produce an
internal secretion which is related to the calcium metabolism.
Their removal, or atrophy, gives rise to tetany, a sudden convul-
sive contraction of the muscles, which may result in death.
The injection of small doses of parathyroid extract usually results
in temporary relief. The effects of too great activity of the

parathyroids have not
been fully ascertained, al-
though it has been shown
by Collip that the injection
of parathyroid extract into
the blood of an animal will
increase the calcium con-
tent of the blood while the
removal of a part of the
parathyroid tissue will give
rise to a calcium deficiency.
Pituitary gland. The
pituitary gland weighs
about one sixteenth of an
ounce 'and is located at the
base of the skull. Galen
and Vesalius knew that
there was a pituitary gland.
They thought it had some-
thing to do with the
secretion of the nose.
(Pituitary is from the
Latin word pituita, meaning phlegm.) Modern experimentation
has proved that there is no such connection or relationship.
There seems to be sufficient evidence to justify the acceptance of

Journal of Heredity
Giantism and dwarfism are probably due to defective
pituitary glands.

THE ADRENAL GLANDS 197

the opinion that the anterior lobe or part of the gland affects
the growth of the skeleton and the posterior part causes several
important bodily changes. Although the hormone or hormones
of the posterior lobe have not been obtained in pure form, in-
jections of extracts from the lobe will cause a rise in blood
pressure, an active contraction of smooth muscles, and a con-
version of glycogen into sugar. Any irregularity in the gland
affects growth, especially that of the skeleton, and the tone of the
muscle cells of the blood vessels. Undersecretion in children
causes them to remain small and fat. Some dwarfs are known
to have very small pituitary glands. These dwarfs are well-pro-
portioned, unlike the cretins with their overdeveloped heads and
abdomens. Too active a pituitary gland in a young person
causes an enlargement of the bones. The individual assumes
giantlike proportions. If the gland is affected in an older per-
son, acromegaly, a gradual enlargement of the bones of the
head, hands, and feet usually results. A rise in blood pressure
and the slowing of the heart beat usually accompanies the
condition.

The adrenal glands. The adrenal glands {ad — on ; renes —
kidneys), called suprarenal bodies by some investigators, are two
small glands situated just above the kidneys. They weigh about
one seventh of an ounce. The inner part of the glands produces a
secretion called adrenin. The secretion, if there is any, of the
outer or cortical region has never been isolated and its function is
obscure. Adrenin, like thyroxin, can be obtained from the gland
in a pure form. It has also been built up or synthesized by chemists
in the laboratory. It is known commercially as adrenaline. Both
the natural and the synthetic product tend to contract the arteries,
thus causing an increase in blood pressure. Visceral arteries are
affected to a greater extent than the arteries leading to the muscles.
Adrenin also hastens blood clotting and strengthens the heart
beat. It stimulates the liver to release the stored sugar. This

198 DUCTLESS GLANDS

sugar is then available for oxidation in the muscles. Thus the
muscles may receive an additional source of energy. The amount
of secretion from the adrenal glands is greatly increased- during
strong emotional excitement such as fear and anger. If a person
is badly frightened, he seems to have unusual ability to escape
from the danger. This is due to the activity of the adrenals
which are stimulated by the emotion, and to the fact that adrenin
is absorbed into the blood stream in unusually large quantities.
The pouring out of the hormone by this gland increases the
blood pressure, strengthens the heart action, and contracts the
visceral arteries so that the, blood supply to the muscles is in-
creased. At the same time, the liver is stimulated to release more
sugar than it would normally. In consequence, the blood supply
brings more food to the muscles which are better able to respond to
the emergency. Fatigue, too, is postponed. This often explains
the great strength people have during an emotional crisis. The
physical endurance of the dancing dervish is an example of adrenal
activity. If physical activity does not result from stimulation of
the adrenal gland, a violent nervous reaction takes place. People
should avoid, as far as possible, situations 'that will arouse
violent emotions, unless resulting activity is desirable. Since

blood is withdrawn from the
islema.o£ viscera during violent emo-

xg-er- a.ns ^ions, grave digestive disturb-
wSe^rts- ances may follow. It has been

demonstrated that mental ac-'
tivity may be seriously inter-
fered with, causing extreme

Certain groups of cells, known as the islands of T1 „ r , m]KnM(!
Langerhans, are a part of the pancreas. They liei vuusiiess.

secrete insulin. Addison's disease, charac-

terized by great muscular weakness, darkening of the skin, low
blood pressure, feeble heart action, and intestinal disturbances, is
attributed, by many investigators, to degeneration or injury of

OTHER GLANDS 199

the adrenal cortex. It is almost always fatal. Removal of the
adrenals in lower animals always results in death.

The commercial product, adrenaline, is used to prevent or check
bleeding. It causes a temporary constriction of blood vessels in
the area, which results in checking the flow of blood. In opera-
tions for the removal of tonsils, surgeons often spray the patient's
throat with an adrenaline solution before the operation, in order
to prevent a great loss of blood. This is known as the bloodless
operation.

The pancreas. The pancreas is a digestive gland secreting
pancreatic juice which passes through a duct to the small intes-
tines, where it acts upon the food particles coming from the
stomach. The pancreas also acts as a ductless gland. Certain
cells embedded in the pancreas, called the islands of Langerhans,
produce a secretion called insulin which contains a hormone that
is absorbed directly into the blood. This hormone stimulates
the liver to give up its glycogen. At the same time, it accelerates
the oxidation of sugar in the tissue cells. Thus sugar is removed
from the blood and the body. If the islands of Langerhans lose
the ability to produce this secretion, the sugar is not used and
some of the extra sugar remains in the blood and some is excreted
with the urine. The individual develops a disease known as
diabetes. Dr. F. G. Banting and his associates discovered (in
1922) that the insulin obtained from the normal pancreas of
animals would produce a marked decrease in diabetes symp-
toms. Much suffering has already been lessened through this dis-
covery. Insulin is available for treatment of diabetes although
it is not considered a cure. Its use must be continual, since as
yet no method has been discovered for stimulating the defective
condition of the organ so that it can make its own insulin.

Other glands. The thymus is a small gland in the neck below
the thyroid. It probably has a close relation to growth and
possibly to sexual development. Experiments seem to prove

200 DUCTLESS GLANDS

that it checks for a time the development of the reproductive
organs. It is very large in a young child, but gradually reduces in
size during adolescence until it is very small in adults. The pineal

body is at the base of the brain behind
and above the pituitary. Extracts from
this gland do not have any observable
effect. There is some evidence, how-
ever, that the injury or destruction of
in a very young infant the thymus this gland in young children is usually
is exceedingly large. followed by abnormal development.

Beneath the diaphragm, behind and to the left of the stomach,
is the spleen. It increases in size after a meal and reaches its
maximum about five hours after digestion. c Then it slowly
decreases to its former size. The cause of this activity is not
known. This gland possibly plays a part in the formation and
destruction of red corpuscles, because quantities of them are
found in it. If the spleen is removed from animals suffering from
one type of anaemia, splenic anaemia, beneficial results follow.

The reproductive glands, also called the gonads, produce a secre-
tion that passes through a duct, and another secretion that is ab-
sorbed directly into the blood. Certain of the cells of these organs
make the sex cells which leave the glands through ducts. This
secretion is dealt with in a later chapter on reproduction. The
normal development of the body depends upon the internal secre-
tion of the sex glands. If the male sex glands or testes are re-
moved from young animals, it modifies the normal course of their
development. Thus we have the normal bull contrasted with the
modified ox and the normal stallion with the modified gelding.
Modified animals never acquire complete secondary sexual
characters.

The secondary sexual characters in man include the beard,
and the large larynx which accounts for the deep voice. After
maturity has been attained, the changes that follow the loss of

OTHER GLANDS 201

the internal secretions are less striking. As old age approaches,
these glands become less active. Great prominence has been
given experiments along the lines of postponing old age by treat-
ment of these glands. These experiments are supposed to affect
senescense, old age, and bring about rejuvenescence, youth and
vigor. Various methods of rejuvenation have been tried ; such
as, grafting glands of young monkeys on human beings or feeding
glandular extracts. All of these methods are still in the experi-
mental stage. Old age is the breaking down of many of the sys-
tems in the body, and it is extremely doubtful whether glandular
extracts will rejuvenate the entire body. To date, the persons
who received the grafted glands showed improvement for a short
time only. The grafted gland was, ultimately, absorbed by the
surrounding tissues. Some scientists attribute the temporary
youthful effects to the optimism and enthusiasm of the subject
rather than a definite physiological effect. The experiments seem
to have some effects, but they are too experimental to discuss as
facts.

Questions and Suggestions

1. Name four diseases related to the thyroid activity. State the
amount of thyroid secretion in each disease.

2. Discuss a diet deficiency affecting the thyroid glands. How has
the resulting disease been controlled ?

3. Account for giantism and dwarfism by glandular activity.

4. Discuss all the physiological activities involved in a dancing
dervish.

5. Name two hormones used commercially. Give the use of each.

6. Make out an outline of the ductless glands and fill in the following
headings as far as possible : (a) Name of gland, (b) Endocrine or
hormone, (c) Use to the body, (d) Disease resulting from over-
secretion, (e) Disease resulting from undersecretion.

7. During a fire, the farmer who owned the house carried a cook
stove from the burning building. After the fire he found he could
not move the stove without help. It took three men to carry the
stove. How can you explain his unusual strength ?

8. What effect does a large cheering section probably have on the
players of a football team ?

WH. FITZ. AD. BIO. — 14

^txmulateoL

CHAPTER XXII

THE NERVOUS
SYSTEM

Mimosa, a sensitive plant.

A leaf that catches flies.

How are 'plants and animals adjusted to their environments f What is
the structure of the brain f What are the functions of the brain f Is
phrenology a science? What scientific studies have been made of the
nervous system?

Irritability. Plants and animals must adjust themselves to their
environment in order to survive. Different conditions in the
environment provoke responses in organisms. Certain of the re-
sponses of the amoeba were considered in the discussion on the
functions of 'the amoeba. If the response is very definite and with-
out exception for a given stimulus, that response is known as a
tropism. Such responses are characteristic of plants and of ani-
mals without a nervous system. In animals with a nervous sys-
tem, if the response is definite, mechanical, and without excep-
tion, the reaction may still be called a tropism. For example,
the swarming of the bees, the fluttering of moths around a light,
and the burrowing of worms into the earth are frequently called
tropisms. When an animal has a well-deVeloped nervous sys-
tem, the responses are more varied and individual. The nervous
system governs and regulates the responses to stimuli. In this
latter case the response is called a nervous reaction instead of a
tropism. The response of the organism, whether it is a nervous
reaction or a tropism, is due to the activity of the protoplasm in the

202

IRRITABILITY 203

individual cells of the active organism. This property of proto-
plasm is called irritability. The possession of this property enables
an organism to make the adjustments necessary for living in cer-
tain environments. Some simple experiments with plants will

demonstrate tropisms

Problem. What response does a plant make to sunlight f
Prepare a box with a series of shelves arranged alternately on opposite sides
so that they overlap each other. The shelves should be several inches apart
and extend into the box about three fourths of the distance. Cut a small
window in the side of the box near the top. Place a plant in a small flower
pot in the bottom of the box. Keep the plant well watered. Place the box
so that the window faces the sunlight and leave it for two or three weeks.
I. A . Describe the growth of the plant, telling how it differs from the normal
or usual method of growth of a plant.

B. What was the value of the shelves in the experiment?
C The response of an organism to light is called phototropism (a turning
to light). Is the response of the shoot of the plant toward or away from
sunlight ?

D. What is the value of phototropism to a plant?

Problem. What is the response of different parts of a plant to
gravity f

Prepare and fill a pocket garden or Petri dish with moist cotton, and place
mustard seeds in a row across the middle of it. Keep the same edge or side
of the garden up until the seedlings have grown to be three fourths of an inch.
After making definite observations, turn the garden to an angle of forty-five
degrees and keep in this position until the plants have grown another three
fourths of an inch. Then make a second examination. Repeat this three or
four times, in each case waiting the number of days required for three fourths
of an inch additional growth before making a definite conclusion and before
turning again. Be sure to keep the moisture evenly distributed throughout
the cotton.

I. A. Describe the direction of growth of the root ; of the shoot.

B. After your first turning what was the result? after the second, third,
and fourth? This response of the plant to gravity is called geotropism.

C. How does gravity affect the growth of the root and of the shoot ?

D. What is the value of geotropism in a plant?

204

THE NERVOUS SYSTEM

Problem. What is the response of plants to water f

Prepare a pocket garden filled with cotton. Plant mustard seeds in a verti-
cal line across the middle of it. Water the seeds by moistening the cotton on
one side of the garden. Try to keep one part of the cotton always moist and
the other part dry.

I. A. Describe the growth of the root and of the shoot. A response to

water is called hydrotropism.

B. What is the value of hydrotropism to the plant?

C. Describe any evidence in the experiment that shows whether gravity
or water is the stronger stimulus.

Z>. If you have ever seen willow trees growing along the bank of a river,
describe how hydrotropism tends to affect their growth ?

The uses of tropisms. Plants make responses to other stimuli.
The response to chemicals is chemotropism, response to heat, thermo-
tropism, and to touch or contact, thigmotropism.

All the activities of living plants and animals involve a series of
responses. As we have already learned, the responses of plants are
definite for given stimuli. Leaves always grow toward the light,

roots grow toward gravity, and

stems grow away from gravity.
Responses are divided into two
kinds of reactions, one toward
the force or stimulus, positive
tropisms, and the other reactions
away from the stimulus, nega-
tive tropisms. In general, tro-
pisms are protective. Without
sunlight, the leaves would not be
able to make starch ; without the
pull of gravity, roots would be
unable to anchor the plant in the
ground. Tropisms help the or-
ganism make the best possible
adjustments to its environment.

Light influences the growth of plants.
Most stems and leaves turn toward the light
and a large area of leaf surface is exposed.

IRRITABILITY IN MAN

205

Irritability in man. In
order to understand the
reactions of man, the
mechanism that brings
about the reactions must
first be studied. This
mechanism is called the
nervous system. It is
often compared to a tele-
phone system. An expert
operator at a switchboard
quickly brings different
rooms in a building, dif-

f + li mpu in n r»I+v Water, also, acts as a stimulus; sometimes it is

ierent nomes in a City, stronger than gravity and causes a turning of roots
different Cities, and even from their normal direction toward the water supply.

different nations into communication by means of messages sent
over various connecting wires. In a similar way, the various
organs of our body are made to work together by means of nerves
that are brought into connection by means of nerve centers.
There are two groups of structures composing the nervous
system : (1) the central nervous system and (2) the sympathetic
or autonomic nervous system. These two systems are intimately
connected with each other.

Protection of the central nervous system. The central nervous
system consists of the brain and the spinal cord. The brain is
covered and well protected by' three membranes which separate
the skull from the skull cavity. These membranes secrete the
cerebro-spinal fluid and contain blood vessels which transmit
blood to all parts of the nervous system. If glancing blows strike
the skull, the movable mat of hair and skin tend to weaken the
force of the blow. In infants, the skull bones are not completely
joined together and, consequently, their brains are not as well pro-
tected as the brains of adults. However, by the time the child is

206

THE NERVOUS SYSTEM

eighteen months old these bones have grown together, forming a
comparatively firm, hard structure. The spinal cord is protected

When the position of the growing plant is changed, gravity again determines the direction of
the growth of the root and of the stem.

by the spinal or vertebral column and moist lining membranes
similar to those in the skull. The vertebral column in an adult,
made up of twenty-six movable bones called vertebrae, permits
flexibility, and gives protection to the delicate spinal cord inclosed.
From both the brain and spinal cord, nerves extend to all parts of
the body. These nerves are embedded in other tissues which
afford them protection.

The structure of the brain. The cerebrum. The larger part
of the brain is called the cerebrum. It is divided into two hemi-
spheres. The outer surface, the cortex, is composed of gray matter

(cell bodies and syn-
apses), and shows
many irregular convo-
lutions. Underlying
the cortex are found
nerve fibers. These
are axons of the neu-
rons. They make up
the white matter.

negative <fe*

geotropism. g^J^

'positive^
geotropisnv

This plant responds to gravity : stems, negatively ; roots,
positively.

Certain definite areas of the cerebrum are concerned with definite
functions. These include motor areas which control movements,

THE BRAIN

207

and sensory areas which are concerned with sensations. Centers
of sensation, motor activities, speech, judgment, reasoning, mem-
ory, and many other activities requiring
thought are located in the cerebrum. Asso-
ciation units link these together and make
possible all kinds of connections. Later, in
considering the activity of the nervous sys-
tem, the cerebrum will be called the third
level.

The cerebellum. Below the cerebrum and
partially covered by it lies a smaller por-
tion of the brain, the cerebellum. This
is the center of muscular coordination and
maintenance of body equilibrium. It may
be called the second level of the central nerv-
ous system.

The medulla oblongata. The brain is
connected to the spinal cord by means of
the medulla oblongata. This is really the
enlarged beginning of the spinal cord but is
considered a part of the brain. It is the
crossing place for most of the impulses to
and from the nerves of the brain. It con-
tains the nerve centers which govern breath-
ing, regulate circulation, and maintain normal
tone of the muscles in the blood vessels. It
controls certain acts such as sneezing, swal-
lowing, vomiting, and blinking.

The spinal cord. The spinal cord, nearly
cylindrical in form, runs through the hollow vertebral column.
It is connected with the brain by the medulla oblongata. The
spinal cord serves as a pathway for nervous impulses from various
parts of the body to and from the brain, and has centers of simple

Ccct

Note the relative size of
the cerebrum in each of the
brains. There is a close re-
lation between size of the
cerebrum and intelligence.
The lower down in the ani-
mal scale, the smaller the
cerebrum and the lower the
intelligence.

208

THE NERVOUS SYSTEM

A photomicrograph of the spinal cord shows
the white matter on the outside, and the gray
matter in the form of anterior and posterior
horns, on the inside.

nervous activities which will
be discussed later. Nerve cells
(gray matter) are found on the
inside of the cord and nerve
fibers (white matter) are found
on the outside. The spinal
cord is called the first level of
the central nervous system.

Cellular structure of the
central nervous system. The
unit of structure of nervous
tissue is a highly specialized
cell called a neuron. It con-
tains the cell body proper, the
cyton, from which fine proto-
plasmic processes (dendrites) extend. One of the processes may
extend a great length and is known as the axon. The dendrites
divide and with branches from other- nerve cells form a mass of
extremely fine fibers. The gray matter of the brain and spinal
cord consists of nerve cells or neurons. Collections of these are
nerve centers. A
number of axons
banded together
constitute a nerve.
Nerves transmit
messages from sense
organs such as the
eye, to the cell
bodies of the neu-
rons, or from the
cell bodies of the

neurons to muscles When the dendrites of two neurons come into contact with

, . _ each other, they form synapses. Nerve impulses travel from

Or glands. ill Order axon to dendrite across one of the many junctions or synapses.

CENTRAL NERVOUS SYSTEM

209

that the nervous system may function as a whole, impulses or
disturbance must readily pass from neuron to neuron. The point
of junction between two neu-

(iencLriteSv
nucleus

CYTON

AXON

rons is commonly known as a
synapse. The sense organs,
known as receptors, receive
the stimulus which starts
the nerve current. The ends
of the nerve fibers of these
organs are on the outside
(skin) of the body. The
muscles or glands are called
effectors because they bring
about activity. An axon
that connects with a sense
organ is called an in-going,
sensory, or afferent axon;
one that connects with a
muscle or gland is an out-
going motor, or efferent axon.
The neurons possessing these
axons may be either sensory
or motor neurons. For ex-
ample, when the finger is
placed on a hot object and
immediately withdrawn, a
series of actions has taken
place in the nervous system. The nerve fiber in the finger re-
ceived a stimulus which it carried to the brain. The brain in
turn sent out a message to the muscles in the arm and hand, so
that the finger was immediately removed from the object.

When neurons connect sensory with motor neurons, they are
called associative neurons. Groups of nerve cells situated outside

The unit of structure of the nervous system is the
nerve cell or neuron. The control of all activities
in the entire body is maintained by these cells.

210

THE NERVOUS SYSTEM

car&iccc
plexus

Solar
plexus

of the brain or spinal cord are known as ganglia. Neurons are
linked together by means of irregular projections of protoplasm,

dendrites, establishing synapses.
The nature of these contacts is
not known. They may be com-
pared with contacts made by two
electrically charged wires. The
type of energy establishing the
contacts in a synapse is nervous
energy.

Autonomic nervous system.
This system is also called the
sympathetic system or self-acting
system. In front of the spinal
cord, and lying parallel to it on
either side of the vertebral col-
umn, are two rows of ganglia,
connected with one another by
nerve fibers. Certain large gan-
glia, called plexus, are also part
of this autonomic system. Three
of the plexus are the cardiac
plexus in the thoracic cavity, the
solar plexus in the abdominal
cavity, and the hypogastric plexus
in the pelvic cavity, but they
connect with many other small ganglia in the thoracic and ab-
dominal regions. The autonomic system transmits some of the
disturbances of the central nervous system to the heart, glands,
and involuntary or plain muscles. Since the viscera (internal
organs) in general are made up of smooth muscle, it follows that
the so-called automatic mechanisms of the body, such as, the beat-
ing of the heart, the contraction and dilation of the muscles, and

••• hypo-
gastric
plexus

The autonomic nervous system consists
of a series of ganglia, most of which are
included in two chains that lie parallel to
the spinal column. These are connected
with nerve centers in the spinal cord.

A very large and unpaired ganglion is
called a plexus.

STUDIES OF THE NERVOUS SYSTEM

211

the secretions of various glands,
are largely under the control of
the autonomic system. Emotions
affect the autonomic system, and
consequently circulatory and glan-
dular disturbances follow or ac-
company emotions. If a plexus is
injured, a violent reaction in cer-
tain internal organs would natu-
rally follow.

Studies of the nervous system.
Scientists have been able to show
that there are many similarities in
the nervous systems of man and other vertebrates. Probably
one of the outstanding differences is the fact that man's cere-
brum is generally larger and heavier, proportionately, than that
part N of the brain of any lower animal. The lower down the

associative
rtexxnoro

spinal
cora

*: spinal
-' nerves

— ctiain, of
gangliac

of autonomic
Systexn-

The ganglia of the autonomic nervous
system are connected with the central
nervous system by nerve fibers.

Sensoi^£
nexxrorv*

/.receptor

Sense
oi^gccn^

TYlotoX^

Tieucron,

muscle

There are three types of neurons. Some take sensory stimulations into the body, others
take motor or glandular stimulations out to muscles or glands to bring about a response. A
third type, known as the associative neuron, may lie between the other two types of neurons and
set up connections between them.

212 THE NERVOUS SYSTEM

animal is in the scale of classification the smaller is the cerebrum.
The convolutions or creases in man's brain are . more intricate
and deeper than those found in lower animals. These convolu-
tions give greater brain surface and contain more functioning
neurons. Scientists once thought that one man was more intel-
ligent than another because one had a heavier brain than the
other. But this does not seem to hold true. The brain of
Cuvier, a great scientist, weighed about four pounds, while that
of Gambetta, a French statesman, weighed only two and a half
pounds. Since mental defectives have been found with brains
weighing more than four pounds, weight alone does not mean
everything. The size and weight of a person must be taken into
account when considering weight of brains.

Neurons never increase in number. The only growth possible
is the setting up of connections or synapses among the different
neurons. The more connections or synapses that are made, the
greater will be the number of mental processes, which is a factor
in determining the intelligence of animals. The ability to make
connections easily seems to be an inherited character. This may
account for the fact that some families have members more intel-
ligent than those of other families.

One of the methods of studying the nervous system is through
experimentation with lower animals. Flourens and others have
observed that if the cerebrum of a pigeon is removed, the pigeon
loses all voluntary or conscious action. It will not move toward
food nor away from danger. However, if food is put into its
mouth, it will swallow. When the cerebellum alone is removed,
balance and coordination become disturbed. The pigeon, if
placed on the edge of a table, will fall. It has difficulty flying be-
cause of a lack of balance and muscular coordination. Its volun-
tary activities, however, are intact. It experiences desire for food,
fear of danger, and other sensations. If the medulla is removed,
respiratory, circulatory, and heart actions cease and the bird dies.

STUDIES OP THE NERVOUS SYSTEM

213

A second method of investigation is by clinical observations and
examination, and autopsies. Doctors observe and examine the

ABSTRACT
THINKINQ

CONCENTRAl/r
f?EASONIN(iZ.L'

1 %

rtfosriff^.

^N^ORX

JO|TpJ^

^ V- TISSUAL AlSEAr

HeAQT.^rXtt
OQCULATlor

According to clinical investigation and animal experimentation, the control of certain physical
functions is localized in definite areas of the brain. There is considerable investigation at
present as to whether there is general control of these functions as well as definite control.
The localization of intelligence, including thinking, association, and memory, is still open to
discussion.

symptoms of people that show nervous disorders, and in many
cases are able to determine the cause of the trouble. When such
patients die and autopsies are performed on the bodies, the doctors
can, in some cases, link up the nervous disorder with the part of
the nervous system showing disease. For example, if a person
had been paralyzed on the left side of the body, the autopsy will
show whether an obstruction, probably in the form of a blood
clot, is on or near the part of the brain controlling muscular
movements. If a person were blind, the autopsy may show injury
to the area of the brain controlling vision.

Certain scientists, through experimentation and study of normal
and of diseased brains, have localized certain areas in the brain.
For a time people carried the idea of localization to an extreme.

214 THE NERVOUS SYSTEM

They thought that a "person's aptitudes and traits of character
could be told from the swellings over these various areas. If one
man had a swelling over the vision area, they assumed that he
could see better than another. If he had a high forehead, they
reasoned that his powers of judgment must be better. Thus the
pseudo-science of phrenology arose. Phrenology, as such, has
been disproved. Careful investigations have shown that the brain
does not conform exactly to the shape of the skull and that bumps
or enlargements on different heads are usually malformations of
the skull and not brain enlargements.

Questions and Suggestions

1 . What is a stimulus ? What is a response ?

2. Discuss an experiment illustrating phototropism ; geotropism;
hydrotropism.

3. What is the value of tropisms to the plant?

4. State the difference between a tropism and a nervous reaction.

5. Name a function of the central nervous system.

6. Discuss the protection of the brain and spinal cord.

. 7. Describe the structure and the function of the cerebrum.

8. Discuss the function of the cerebellum ; the medulla oblongata ;
the spinal cord.

9. Describe in detail the unit of structure of the nervous system.

10. Draw and label a neuron. Name and define three types of
neurons.

11. What are nerve centers and ganglia ?

12. Compare the brain of man with the brain of lower animals.

13. Discuss two ways of studying the nervous system.

14. Describe the structure and function of the autonomic nervous
system.

Supplementary Readings

Gates, A. I., Elementary Psychology (The Macmillan Co.).
McDougall, W., Outline of Psychology (Charles Seribner's Sons).

SKl*"!

CHAPTER XXII I

NERVOUS
REACTIONS

Ancient idea of the human
nervous system.

Present idea of the human
nervous system.

What mental activities are learned and wliat are instinctive f
is a habit t What is the best method for learning facts t

What

When tropisms were discussed, the importance of stimuli was
stressed. As in plants and lower animals, it is a stimulus in a
higher animal that starts the nervous impulse which results in a
typical reaction. This impulse may be any one of three types of
mental activities : (1) inborn automatic, (2) acquired automatic,
and (3) voluntary.

Reflex activities. There are certain motions and acts that a
baby performs soon after it is born. These responses are simple
reflexes or inborn automatic activities. The child does not have to
learn or acquire them. Some of these responses may involve the
brain, while others are controlled only by the spinal cord. The
child comes into the world equipped with pre-formed connections
or tendencies to connections in his nervous system. In other words,
nervous pathways or patterns are already set up. A new-born
baby that has not learned to think will pull his foot away if
pricked with a pin. He will sneeze if his nostrils are tickled with a
feather, and will grasp a finger if it is placed on the palm of his tiny
hand. Each of these responses to the given stimulus is a reflex.
If a person swings one leg freely over the other and taps it just

215

216 NERVOUS REACTIONS

below the knee cap, the tap will cause the knee to jerk. In this
experiment, the stimulus is received by a nerve ending in the skin.
The stimulus starts an impulse which travels along a sensory
neuron into the spinal cord. There, this sensory neuron links up
with an outgoing motor neuron by means of a synapse. The out-
going neuron conveys the impulse to a muscle in the leg, which
causes the knee to jerk. In some way, the in-going sensory stimulus
is changed into an outgoing muscular reaction. The sense organs,
in this case " touch spots " in the skin, receive the stimulus and are
the receptors. The muscle effects the reaction and is the effector.
The pathway of the receptor, composed of the afferent axon, affer-
ent cyton, synapse, efferent cyton, efferent axon, and the effector
make up the reflex arc. Any reflex arc involving the central
nervous mechanism begins and ends in the outer part of the body.

Types of responses. The simplest response activities involve at
least two neurons. Experiments have been made with frogs
whose brains have been severed from their spinal cords. Such
frogs lose all conscious activities, but are still capable of making
certain reflexes. If the toe is pinched, the leg is withdrawn;
violent pinching causes a distinct jump. If a paper wet with
dilute acetic acid is placed on the skin of the leg, the frog makes
movements to brush off the paper.

If the foot of a sleeping baby is tickled, the foot is withdrawn.
This is a reaction or reflex of the first level. The impulse, caused
by the stimulus, passes into the spinal cord and out again without
involving any other connections. The knee jerk is another ex-
ample of a reflex of the first level. But, if the blow on the knee
is severe enough, the person may gasp or. scream or balance him-
self to preserve his equilibrium. He may even show an increased
heart beat. The centers of respiration and circulation are stimu-
lated, and balance and coordination are brought into the action.
This response is of the second level. A number of neurons enter
into this activity. Some of them are sensory and a great many

CONDITIONED REFLEX 217

are motor, which result in a number of reactions. Reactions of
the second level are more complex than those of the first level
and will involve parts of the
body somewhat distant from
the point of stimulation.

When the knee jerk
arouses thought or delibera-
tion, it is classified as a third A reflex arc is traversed when the finger touches
11 p i a nail. The sense organ in the skin is stimulated,

level response, r Or example, the stimulus is carried over the afferent or sensory
if +Tip Klnw i« en qpvpw neuron through a synapse to a motor neuron. This
ii u.ic uiuw io bu bcvcic ends in a muscle which contracts and causes the

that one would rub the in- fln « er to be puUed away *
jured spot or examine it deliberately, certain neural connec-
tions would be made in the brain. Such consequent thoughtful
activities attend the reflex so closely that they are sometimes con-
sidered a part of the reflex. Such reaction is called an activity of
the third level.

Conditioned reflex. A baby is born with the pathways for a
certain number of reflexes already established. When certain sense
organs are stimulated, the impulses travel along these pathways
until they reach muscles or other mechanisms, which carry on the
processes essential for maintaining life ; such as, sucking, digesting
of food, crying, coughing, and moving. When these responses
are caused by other than the original stimuli, they are said to be
modified or conditioned. For example, Pavlov, a Russian physiol-
ogist, observed that the secretion of saliva in a dog is a reflex act,
resulting from nerve pathways established in the dog at birth.
The appearance of food or the taste of food in the mouth acts as the
stimulus, and the flow of saliva is the response. If the same person
always feeds the dog, the saliva of the dog will, after a certain
number of times, flow at the sight of that person even though no
food is given. The stimulus in this case is the sight of the person,
not the food, and the response is the flow of the saliva. The
response occurs in the hungry animal even when it can neither see

WH. FITZ. AD. BIO. — 15

218

NERVOUS REACTIONS

nor smell any food. The animal has evidently acquired a new re-
flex path. The acquired reaction is conditioned upon a memory

association which con-
nects the presence of a
certain person with the
eating of food.

In another experiment,
a bell was rung, and ex-
actly two minutes later
food was given a dog.
Ultimately, after the ex-
periment had been con-
tinued a long time, the
saliva flowed in the dog's
mouth exactly two min-
utes after the ringing of
the bell even though no
food was given. This could be carefully measured because of
a little tube that was injected into the duct leading from the
salivary gland of the dog. Saliva could be seen flowing from the
duct exactly two minutes after the ringing of the bell. Sparrows
usually build nests in the gutters and holes in barns and houses.
Building the nest is inborn, but buildings have not existed as long
as nest-building, so nesting in houses must have become conditioned

cerebellum.

-mc&ulloc
oblongata

-spinal

The three levels of the nervous system are shown
here. The first level is in the spinal cord, the second
level is in the cerebellum, and the third level is in the
cerebrum.

■receptor

by buildings. Conditioned
responses depend upon
associations formed in the
cerebrum. Injury to a
certain part of the cere-
brum of a dog with a con-
ditioned response has caused the ability of the animal to respond to
the stimulus to be entirely destroyed.
The original reflexes that are a part of the organism at birth are

sensory neuron

In a reflex of the first level, the center of control is
the spinal cord. This is the simplest type of reflex.
The response is usually very simple.

VOLUNTARY ACTIVITIES 219

evidently not fixed and invariable but are flexible and modifiable
and may become changed or conditioned by factors in the environ-
ment. The organism begins to in&bm'm mvscie
relate factors in the environment
to his activity. This results in
the changing of the original re-
flex. Certain acts may be con-
sciously inhibited, that is, di-
verted or blocked. For example,
a child instinctively makes known
his wants by crying. He has
learned that when he cries, he has Teuton S£> rfl 1 * effector

always been picked Up. One day, In response of the second level, centers
U XX J j.l~ • J j. m tne spinal cord and mid-brain exercise

ne Unas that Crying does not control. A number of activities will re-
bring the desired attention. He sult '

stops after a while, and, in time, learns to express his wants in
another way. The changing is due to consciousness. It probably
explains the beginning of the learning process or conscious acts.

Voluntary activities. Any act involving will or thought is a
voluntary act. The name " voluntary " refers to the will. All
activities, excepting the so-called inherited reactions, performed
for the first time are voluntary acts of the will. When the
activity requires attention, memory, judgment, or association, a
great many associative neurons are used. For example, the hand
is put in water and is held there while a decision is made as to
whether the water is of the desired warmth. Then the hand is
withdrawn. The sensation is received by the skin as the receptor.
The impulse travels along an afferent axon to the spinal cord, up to
the brain. A number of neurons located in the brain are stim-
ulated, bringing about a condition of consciousness, and resulting
in attention. Meaning becomes attached to the sensation that has
been received and a mental decision is possible. A comparison may
be made with previous water used in washing ; the thought may

220

NERVOUS REACTIONS

level

occur that injury will result in casejt is too hot; a consideration
of the fact that cold water will not cleanse may be involved.
Finally a decision is made. Then a connection is made with a
motor neuron. The impulse goes down the efferent axon to the
muscles in the hand and the arm, which are the effectors of the
activity and the hand is withdrawn from the water. In many
instances, the learning of facts such as rules of grammar is im-
possible without attention. Attention is partly dependent upon
inborn tendencies and partly upon acquired habits. The more
closely the activity is related to the child's life and the more
associations he can make, the easier it will be for him to remember
the facts. For instance, if a child lives in a city, it will be easier
for him to understand the problems of city government and traffic
conditions, than for the child who has always lived in a rural

community.

Acquired automatic ac-
tivities. Activities which
are learned in a person's
lifetime, but have become
automatic through repe-.
tition, are acquired auto-
matic activities. For ex-
ample, brushing the teeth
is an act that had to
be learned. By directing
attention and thought on
the action the first few
times the teeth were
brushed, definite tech-
nique and skill were soon
gained. The receptor
was the gums of the mouth. When the toothbrush was placed
in the mouth, a sensory axon took the impulse into a sensory

effector-
of second
lfevel
-resporLSe.

Rector* ©P

thira. '
level

effected of
fttwt Wei

A third-level response uses neural connections in
the brain. Psychologists think that all learned reac-
tions are dependent upon connection established in the
brain level.

THE AUTONOMIC SYSTEM 221

neuron of the cerebrum. As the child thinks whether he shall
brush the teeth, up and down or across,, whether his mouth should
be open or closed, whether he should lean over the basin or not*,
connections are set up among association neurons. Finally, he
comes to a decision. An impulse is sent along an efferent axon
down the spinal cord and into the muscles of the arm which are
the effectors. The actual brushing of the teeth is the motor
response. The correct response was consciously made. This is
an act of the third level involving the cerebrum. After the teeth
have been brushed a number of times, the decisions and the asso-
ciations are no longer necessary. While the act was conscious,
inhibitions Jn the nervous system blocked certain paths of con-
duction between the sensory stimulus and the motor response. As
the act was repeated, time after time, these inhibitions disappeared,
and the act was easier to perform. The more times the impulse
passed over the pathway of discharge, the less was the resistance
to it. After this reaction was learned a synapse was set up be-
tween the afferent and efferent pathways, leaving out some of the
association neurons. In some habits the pathway is essentially the
same, but consciousness is omitted. It has become automatic and
has descended to the second or possibly the first level. It is now
an acquired automatic activity involving no thought and is com-
monly called a habit. Habits are frequently defined as acts which
were first done in a typically voluntary way, but after sufficient
repetition they are done in a comparatively reflex way. Memory
is most important in changing conscious acts into habits.
. Importance of the autonomic system in nerve activities. The
internal organs, in general, are under the control of the autonomic
nervous system. The autonomic system controls the contractions
and relaxations of the smooth muscles. It regulates glandular ac-
tivities and heart action. Emotions activate the autonomic sys-
tem. If an emotion such as fear or anger accompanies a reflex act,
habit, or a conscious act, the autonomic system enters into the

222 NERVOUS REACTIONS

activity. There will then be attending respiratory, circulatory,
and glandular activities. For example, a rabbit sees a cat and
fries to escape. The sensory stimulus is the sight of the cat while
the reaction is the motor act of escaping. Because fear attends
this voluntary act, the autonomic centers of the rabbit are stim-
ulated and their resulting activities favor the response of out-
witting the cat. The bronchial tubes of the frightened rabbit are
relaxed and rapid breathing is made easier. The contraction of
blood vessels in the viscera and the increased heart action forces
more blood into the skeletal muscles. Thus, extra oxygen and
fuel are supplied to the muscles. The 'nerves stimulate the
adrenal glands which pour out their secretion into the blood,
causing the liver to give up more sugar into the blood, as well as
increasing the endurance and strength of the muscles and reducing
the activities of digestion. The rabbit has more energy than
normally and is able to run faster from the cat which is activated
purely by the instinct of hunting. But, if the cat is aroused by
a strong feeling of hunger, we would find in her activities very
similar to those in the rabbit. In this case, the probability of
escape by the rabbit would be lessened.

The nature of the nerve impulse. The nature of the nerve
impulse is not fully understood. The speed with which it travels
along a motor nerve fiber is about three hundred and ninety feet
per second. The time elapsing between the application of a
stimulus and the response varies in different individuals and in
the same individual under different conditions. It depends upon
the strength of the stimulus. If the stimulus is very strong the
response will be prompt. If the stimulus is weak the response
is not made or is made very slowly. The time of reacting is
dependent upon the nature of the stimulus. For example, the
response to a person walking toward you is quite different from
the response given when an automobile comes toward you. The
time is also affected by the number of synapses through which the

IMPORTANCE OF REACTIONS 223

stimulus has to pass. If the nervous pathway is long, a propor-
tional length of time is required for a response. Removing your
hand from a hot stove requires less time than deciding which way
to jump when you find yourself in the path of a fast moving car.

The importance of reactions. The patterns of behavior formed
almost immediately after birth are called instinctive or innate acts.
These include the avoiding reactions such as struggling when
held, and withdrawing from or rejecting anything that is causing
discomfort, as moving the leg if it is being pinched; and the
approaching reactions or movements caused by hunger and by the
stimulation of certain sensitive parts of the body, such as, tickling
the bottom of the feet or rubbing the back. These reactions or
established patterns are frequently modified to meet changing
conditions. For instance, a small child will usually push away
or strike at a person who annoys him, but later he will modify
his tendency because the group he lives in demands a different
method of reaction. He will learn to respond to reason and not
follow his instinctive desire to fight.

Habit formation. When voluntary activities are made habitual,
they are performed more easily and quickly. When completely
established, they act the same as instincts. When activities be-
come habits the brain is not needed and it is then set free to make
new responses or activities. This results in the growth and de-
velopment of the mind or consciousness. If the attention were
concentrated on the daily performance of brushing the teeth,
dressing, walking, and other necessary activities, the mind would
be occupied continuously on acts that are necessary for mere
existence. The possession of useful habits sets the mind free to
attend to the gaining of new knowledge. Individual progress
may be said to be dependent upon the ability to acquire habits.

There are three rules for making conscious activities, such as
combing the hair, or starting an automobile, habitual. First,
there must be concentration on the performance of the act.

224 NERVOUS REACTIONS

When there is a real desire to build the habit, it is more easily
formed. Second, the activity must be repeated a number of times
under exactly the same conditions, permitting no exceptions to the
performance. Third, the act becomes automatic niore quickly if
feelings of satisfaction attend the performance. If any annoyance
accompanies the performance, it delays the forming of the habit.
If exceptions are made in the type of reaction, judgment again
enters into the performance and it continues as a thoughtful act
rather than a habitual one. In performing the act each time in
exactly the same way, the same nerve padi is traversed. Then
when the stimulus is received, the impulse goes more quickly over
the pathway, and synapses connect up with greater facility.

In order to break a bad habit, there must first be a sincere desire
to get rid of it. The activity must be brought back to conscious-
ness so that the will may be directed on breaking it. For example,
in order to break the habit of biting the nails, red pepper may be put
under the nails. The sharp biting effect on the tongue will bring
to consciousness the fact that the nail is in the mouth. Each time
the person realizes that the nail is in the mouth, he must take it
away from the teeth and there must be no exception to this reac-
tion. The person who says he cannot break himself of a bad
habit means he does not want to break it. If the growth of the
nail and the improved appearance of the hand brings satisfaction,
the habit of refraining from biting the nails will be more speedily
established. The most effective way of breaking a bad habit is
to substitute a good habit which will be more satisfying than the
bad habit. For example, if a boy has formed the habit of standing
on a street corner in the evening, he may find that joining an
athletic club will be so satisfying to him, because of its activities
and congenial companions, that in a short time his old habit has
lost its influence altogether. It is not wise to ever perform an
idle or vicious voluntary act, for if a synapse has once been es-
tablished between two neurons in performing an act, it is easier

HABIT FORMATION 225

for the nerve impulse to go over this pathway a second time.
There is always the danger of an undesirable voluntary act be-
coming habitual. The years of childhood are the critical ones in
habit formation and, therefore, in character building; childhood
habits form the basis for later conduct. If the acquired habits
are later found to be undesirable, it is necessary to make substitu-
tions and this is a waste of mental energy. Consequently, it is of
the utmost importance to build correct habits by the proper con-
ditioning of reflexes in the beginning.

To a large extent, mental growth results from acquiring a large
number of useful voluntary activities. Prpbably every one has
the same number of neurons. There is an infinite number of
possible connections among them. The same neuron may link
up with several others and this may result in a great many different
activities. As each new act is performed, a new combination of
neurons is connected by means of synapses. The more synapses
are made, the greater will be the growth in experience, judgment,
memory, and reasoning. If any voluntary act which is useful
can be relegated to the realm of habit, it will give greater oppor-
tunity for acquisition of new voluntary acts.

Problem. The study of nervous activities:

List twenty simple activities performed by you in one day. Next to each
activity put the class in which it belongs : inborn automatic, acquired auto-
matic, or voluntary.

I. Which of the voluntary activities listed would be desirable as habitual
ones? Why?

A. What prevents them from becoming habits?

B. How may they be changed into habits?

II. How can you improve the performance of any act in your life?

Questions and Suggestions

1. What is a reflex arc? Make a labeled diagram of the reflex arc.

2. Name three types of nervous activities.

3. What is the value of reflexes to the organism ?

226 NERVOUS REACTIONS

4. To which activity is a tropism comparable ?

5. Draw and label a diagram of a reflex activity.

6. Explain and give an example of the conditioned reflex. What
scientist has been investigating it ?

7. How could you make learning to swim a habit ?

8. Make a labeled diagram of an acquired automatic activity.

9. Explain how the habit of biting the nails may be broken through
(a) inhibition, (b) substitution. Explain which method is the more
desirable method.

10. Why is it possible for people to break themselves of bad habits,
if they have an earnest desire to do so ?

11. Discuss the advantages and disadvantages of adopting a child
of six months ; of five years ; and of fourteen years of age.

12. Give examples, from your own experience, of habit formation,
and discuss the importance of attitude as an aid and as an interference.

13. What is the value of a habit of regularity ? Of concentration ?
Of thoroughness ?

14. What is the relation between habit formation and vocational
success ?

15. What is the importance of voluntary activities ?

16. What is the function of the autonomic system?

17. Discuss the value of basing education on what a child wants
to know rather than on what an adult thinks he ought to know ? Should
a child study only those things he wants to know ?

18. What is the relation of interest and attention to understanding ?

Supplementary Reading
See Chapter xxii.

CHAPTER XXIV

MENTAL
HYGIENE

Some like to paint —

Others enjoy a swim.

What relation have psychologists found between intelligence and suc-
cess f How can the nervous system be kept in good condition?
What may be the effects of worry, fear, temper, and introspection f

The ability to meet and solve the problems of one's life without
needless worry, leads to serenity, contentment, and happiness.
The solution of problems brings a joy of achievement that is con-
ducive to greater success. The boy whose problems are decided
for him does not find the contentment nor achieve the poise that
is attained by the boy who faces and solves his own problems.
Poise is usually considered one of the constituents of. success in
the varied and complex life of the present day.

Intelligence. Intelligence may be defined as the native capacities
of a person to learn, to reason, to exercise mental control, and to
solve his life's problems. Can a child be apparently dull or back-
ward for a number of years and suddenly become highly intelli-
gent? Scientific experimentation seems to prove that certain
mental capacities are native or inborn. If a child of six years of
age is found, experimentally, to be of average intelligence, when
measured by certain tests, he will, with very rare exceptions, be
found to have average intelligence at seven years, eight years, and,
in fact, all through his life. If a child of six years tests below aver-
age, the chances are that he will remain at that level all through life.

227

228

MENTAL HYGIENE

•40JK

15$ 20#

0,5%

C+

46^ '9%

Intelligence of these, meru
as ^termme5Llythe0lphatfest

The Army Alpha test was given to 1,700,000 men in
the United States army in the World War. It con-
sisted of 212 questions. Grade A was given to those
answering correctly 135 or more of the 212 questions;
grade B for 105 to 134 correct answers. A was earned
by only 4.5% of the men. Compare the results attained
by the other groups of men as shown in the table.

The scientific measurement of intelligence, most frequently used
as individual tests, is a series of performance tests arranged in the

order of difficulty. The
first of such tests was
worked out by two French
psychologists, Alfred
Binet and Theodore
Simon. These tests have
been, revised by different
persons in America, and
among these revisions is
one by Terman, known
as The Stanford Revision
of the Binet-Simon Scale.
This scale includes tests of
memory, language com-
prehension, size of vocab-
ulary, knowledge of familiar things, judgment, and many other
mental tasks that are a part of every child's experience. Stand-
ards, to show what children of certain ages should know, have been
established by comparisons of the results or ratings made by chil-
dren of definite ages in all sections of the country. For instance,
there are a certain number of questions that a six-year-old child is
supposed to answer correctly. If a particular child of six answers
less than this score, he is said to have a mental age, M.A., of four
or five, or whatever age that score is supposed to measure. If he
answers more than the required number, he may have a mental
age of seven, eight, or even more. Thus there are tests ranging
in difficulty from those for a three-year-old child to those given
to an adult. For the practical purpose of measuring progress in
school the intelligence quotient, I.Q., is used. This is obtained by
dividing a child's mental age by his age in years. This quotient
will usually remain fairly constant from year to year, for his men-

RELATION OF INTELLIGENCE TO PROGRESS

229

tal age will grow or increase as he becomes older. The average in-
telligence quotient for any given age is 100. For example, a pupil
has a mental age of six, according to the Stanford Revision Scale,
and his age in years is six. Divide his M.A. 6 by his real age 6
and the intelligence quotient will be 1.00. (This I.Q. is usually
expressed without a decimal, as 100.) Another pupil of 6 has a
mental age of five and a half and his real age is six. Dividing his
mental age, five and a half, by his age in years, six, we find that
he has an intelligence quotient of 92. If a pupil's mental age is
eight and his age in years (chronological age) is six, his intelligence
quotient is 133. The I.Q. of the average high school graduate
probably ranges from 90 to 105.

Relation of intelligence to progress in school. In general,
pupils who have low intelligence quotients have difficulty in
making progress through
school. When pupils with
high intelligence quotients
have difficulties with their
studies, it is usually due to
physical defects, irregular
attendance, late entrance,
refusal to study, or some
other remediable condition.
If a child is retarded in
school, even though he puts
forth sincere efforts, and
there is no remediable con-
dition interfering with his
school work, then he should
be given a different type of
schooling. Various voca-
tional schools are endeavoring to provide courses for such children,
so that they may take subjects which they can understand and in

\b%

left school 4 gfcacte

137$

i4r£

<o •

27# 7+8 -

25?^ aft*r8 -

io#

enteral Ki^h school

gto&xxoted. college

The schooling of the American population has
been graphically described in the above table. This
is based on a report of the Department of Labor.
Compare the distribution of schooling in this table
with the distribution of intelligence in the preceding
table.

230

MENTAL HYGIENE

current,

"nerve*,
muscle

which they can achieve success.
If a child is permitted to fail
term after term, he falls into
an attitude of mind which de-
stroys his confidence and he
makes only a half-hearted
effort to succeed. He gets the
habit of failing. The pupils
who reach high school are, to
a certain extent, a selected
group, because the dullest pupils
have become discouraged and
dropped out. Education re-
sults in the growth of experi-
ence or mental age, but not
native ability.

Relation of intelligence to
vocations. Individuals who
rate low in the intelligence tests are not, necessarily, undesirable
members of society. There are relatively few children so dull that
they cannot succeed in some line of work. Many failures and
much discontent are due to the fact that boys and girls sometimes
enter vocations that require too much or too little intelligence in
relation to their mentality.

The leg muscle of a freshly killed frog is at-
tached to a lever. It is stimulated through the
nerve by means of a make and break electric
current. A tracing of the contractions is made
on a, revolving drum. At first the contraction
is very decided and regular. Slowly the re-
sponse decreases until the muscle ceases to
react. Rest or washing the muscle will start
the response anew, but in a short time fatigue
again is apparent.

Record made on a revolving drum by a stimulated frog's muscle.

In an experiment conducted by J. K. Flanders and reported by
Terman, the intelligence of a group of employees of an express
company was tested. These people were employed to do work
that required about the same level of mental ability. It was

A HEALTHY MIND

231

"found that their intelligence, that is, their I.Q., ranged from sixty-
two to one hundred and four. This work could have been done
efficiently by persons with scores of ninety. C. W. Waugh^ave
intelligence, tests to eighty-two street-car motormen and con-
ductors. The investigation showed a range of intelligence from
sixty-five to one hundred and ten. A score of eighty to ninety
was probably sufficient for a person to do this type of work well.
Those with higher intelligence did not do more work nor do it
more efficiently than those of lower intelligence. One of the
men scoring low had a serious accident on his car. It is a
fairly well-established fact that a motorman or conductor with
an I.Q. of less than/ seventy-five is, as a rule, an unsafe risk.
There is a big economic loss, to the company as well as the indi-
vidual, in employing men of high intelligence to do work that
could be done as well by men with less intelligence. Educators
should direct those students of highest I.Q. ratings into lines of work
which will require superior intelligence, and those of mediocre in-
telligence, low I.Q., into lines

nucleus*

of work for which they are
fitted. At present, there is
too great a waste of mental
ability by men and women
filling positions that could be
competently filled by persons
of less ability. Students
studying professional subjects
should be those of fairly high
intelligence rather than
merely those with money
enough to pay for such train-
ing.

A healthy mind. The nervous system, like the other systems
of the body, is kept in the best possible condition if the body is

fc^toplasm^ 7

A tired nerve cell (B) shows fewer chromatic
granules than a rested nerve cell (A).

232

MENTAL HYGIENE

^*f^

Idleness does not bring satisfaction for any
great length of time. It is, frequently, the result
of bad habits and usually, if not always, leads to
inefficiency.

kept healthy by fresh air, good
food, sleep, rest, sunlight, and
exercise. The nervous system
is probably more sensitive to
the lack of any one of these
conditions than any other sys-
tem in the body. A change of
activity is frequently bene-
ficial. Otherwise,, a person
may become physically as well
as mentally fatigued, thus
greatly reducing his efficiency.
Every person should have a
hobby and follow it as much as
possible. A hobby that takes
him out of doors is more de-
sirable than one that keeps
him indoors. People with hobbies are usually able to make use
of their leisure time in a way that is enjoyable as well as bene-
ficial to them.

Fatigue. Prolonged or continued contractions of muscles in
any kind of work result in fatigue. This condition is almost
always followed by a steady decrease in efficiency. The feeling of
fatigue is very complex and is often associated with such mental
states as lack of interest, lack of will power, and distaste for the
work. Work done under compulsion usually results in fatigue
more readily than when interest is a part of the work. This is one
reason why e,very one should do the kind of work which he really
likes.

Experiments have shown that if some blood of a fatigued animal
is injected into a rested one, signs of fatigue are promptly produced
in the second animal. Fatigue is probably due to an accumula-
tion of waste substances in the cells and in the blood, resulting from

MENTAL POISE

233

the oxidation process. If these accumulate faster than the organs
of excretion can eliminate them, they are likely to act as poisons.
At the same time, the food material in the cell becomes exhausted.
Because all bodily activities are slowed up during sleep, the sleep-
ing organism has a chance to eliminate the accumulated wastes.
The repair of all tissues goes on during sleep. It is the muscle
cells and brain cells, particularly, that become fatigued. In
monotonous work the same neurons are constantly being used.
This work should be counterbalanced with some kind of recrea-
tion. Rest and play balance mental work because different path-
ways are traveled. Fatigued synapses offer resistance to impulses.
This naturally results in inefficiency or lack of activity. A high
school boy or girl should sleep, approximately, nine hours a night
in order to efficiently restore fatigued nerves and muscles.

Mental poise. Mental hygiene has for its object the promo-
tion of mental poise and serenity, and the prevention of mental
disorders. Nervous instability is shown by a predisposition to
strong emotions that are easily aroused and are only controlled
with difficulty. Worthless n-*
nervous activities should be
eliminated as far as possible
by cultivating proper atti-
tudes. Worry and fear stimu-
late certain parts of the auto-
nomic nervous system and may
have injurious physiological
effects. Strong emotions tend
to stimulate the adrenal glands,
causing the withdrawal of
blood from the viscera. This
may result in serious digestive
disorders. Worries exercise neurons with no worthwhile gain.
Frequently, the worry is over an act that is beyond control. For

WH. PITZ. AD. BIO. — 16

A hobby gives one a satisfying way of spending
leisure time. The more interesting and novel is
the hobby the greater will be the resulting satis-
faction.

234

MENTAL HYGIENE

example, people worry whether or not it will rain ; whether or not
they will be struck by lightning ; whether or not they will be hit

The frame of mind with which one enters into an activity directly affects the results. Cheer-
fulness towards duty is a desirable attitude to cultivate as it tends to* bring about greater
efficiency and mental poise.

by an automobile. If a condition is recognized as beyond control,
thought of.it should be put out of mind. Nothing can be done
about it. Mental energy should not be wasted.

Another type of worry is closely akin to fear. Some persons are
afraid they will not pass an examination ; others are afraid of the
dark, or of a neighbor's criticisms. The only way to control these
worries is to face them fairly and think them through to a conclu-
sion. In practically every case, the fear or worry would not exist if
the problem had not been avoided in the beginning. For example,
the refusal to study will, in most cases, result in a fear of failure.
When children face the painful consequences of conduct, accept
failure or blame at face value, decide about problems rather than
evade issues, face their difficulties squarely, and make a decision,
they achieve mental poise. If the nervous energy consumed in fear
were put into solving the problem, it would be used to a better
advantage and the person would be happier. If one is afraid of
failing in an examination, he should find out the cause of his fear.
Possibly, the solution is to work harder. Possibly, the pupil is

MENTAL DISORDERS

235

beyond his grade. If so, he should recognize the conditions and
ask to be demoted. The effect of the failure is worse than^the
demotion. If afraid of the dark, one should investigate the dark
place and see how unreasonable is the fear. If the mind is kept
occupied with useful and cheerful thoughts, fears and worries
disappear. Fears in children as well as in older persons may be
overcome by a quiet reassurance and a reasonable, sympathetic
investigation.

Bad temper is frequently an excuse for inefficiency. It is a way
out of an annoying situation. If, instead of giving way to moodi-

Strong emotions are frequently shown in facial expressions. Note the facial expressions in
the picture and try to determine what emotion is registered in each.

ness or temperament, the person tries to understand the difficulty
confronting him and tries to think out a solution, a normal re-

236 MENTAL HYGIENE

sponse will follow. These normal responses help to develop
proper attitudes. If one once recognizes that bad temper is
futile, that it is wasteful of emotion, and that it interferes with sane
reasoning, he will overcome it. It is particularly valuable to think
things through to a conclusion and to keep a sense of humor. These
are invaluable in overcoming nervous difficulties and building up
an optimistic view of life.

Introspections are usually to be avoided in adolescence. When
one thinks about himself, it is from so emotional and prejudiced a
viewpoint that a fair judgment cannot be made. Day dreams
may be conducive to success. They may make one ambitious and
spur him on, if he dreams of achievements. But, if imaginary
slights are exaggerated and dwelt upon, such thinking leads to
mental disturbances. Social intercourse with other children, par-
ticularly in free play, is especially desirable in order to help a
child adjust himself in the social group in which he must live.

A feeling of inferiority is a symptom common to a disturbed
nervous system. When children are laughed at, or spurned, or too
severely criticized, they lose their self-confidence and their self-
respect. This feeling of inferiority inhibits effort and causes dis-
satisfaction, unhappiness, and possibly failure. Responsibilities
should be given such children. Confidence, respect, and whole-
some consideration should be shown their efforts, so that they will
make proper efforts toward success. Children should be able to
take effective action when necessary.

Self-pity and lack of confidence are also undesirable. They may
come from trying to accomplish things that are too difficult or are
beyond the mental ability. Talking over problems with a person
whose judgment is valuable and worthwhile, often helps to direct
a person's activities along the proper lines. It reduces strain and
worry and prevents the repression of thought.

Effects of Tobacco and Alcohol on the Nervous System. There
is a distinction to be made between the effects of tobacco upon

EFFECT OF TOBACCO ON NERVOUS SYSTEM 237

young people and adults. Many school records show that, in
general, smokers have lower scholastic standing than non-smokers.
The use of tobacco in early youth forms a habit that becomes
increasingly hard to break and in many instances has harmful
effects upon the general ability of the person.

Tests have been made to see the effects of alcohol on mental
and motor achievements. One of these tests showed that after
a person takes alcohol in any form the rate of his pulse is
increased, steadiness is decreased, coordination is lessened, and
his ability to add is decreased. In all the tests that have been
made, alcohol appears to reduce functional capacity. Recent
tests show that alcohol is not a stimulant but a narcotic. The
apparent stimulation following the taking of alcohol is due to the
deadening of the nerve centers of control. The higher nerve
centers of judgment and decision become dulled, resulting in irre-
sponsibility. The memory tests which were conducted showed that
seventy per cent less work was done when the subject was using
alcohol. Many industrial organizations, railroads, and mercantile
houses require their men to be total abstainers. The experience
of these, corporations proves that alcohol interferes with efficiency
and is directly responsible for many accidents. The investigation
of these two drugs is still largely experimental.

Questions

1. What is the relation of intelligence to school progress?

2. What remediable conditions may cause failure ?

3. What can be done with dull children ?

4. How do you think that it is possible for psychologists to deter-
mine the intelligence necessary for efficiency in various positions ?

5. What precautions are necessary for keeping the nervous system
in good condition ?

6. What is fatigue ? How can it be overcome ?

7. What are the objections to worries, fears, bad temper, and
introspection ?

8. What can be done for a person with an inferiority complex ?

238 MENTAL HYGIENE

9. What is the value of play, leadership, and success to a child?

10. Why do some people dislike their work ? Is it possible to rem-
edy this condition?

11. Criticize the habit of debating with oneself without coming to
a decision.

Supplementary Readings

Burnham, Wm. Henry, The Normal Mind (D. Appleton and Co.).

Gates, Arthur I., Psychology for Students of Education, Chap, xviii (The

Macrnillan Company).
Robinson, James Harvey, Mind in the Making (Harper Bros.).
Terman, L. M., Intelligence of School Children (Houghton, Mifflin Co.).
Wiggam, Albert Edward, Exploring Your Mind (D. Appleton and Co.).

CHAPTER XXV

HOW
LIFE BEGAN

Louis Pasteur.

His flask of nutritive fluid.

What was one of the ancient ideas of the origin of life? How and
by whom was the theory of spontaneous generation disproved? How
do some scientists of to-day explain the origin of life f

The ancient idea of the origin of life. At the time of Aristotle,
and for many centuries following the work of this Greek teacher
and philosopher, there was a theory, supported by scientific men,
concerning the origin of life, and known as spontaneous generation.
According to this theory, living things rose spontaneously from
non-living materials. Bees were supposed to come from the dead
bodies of young bulls; young rats could be made to appear in a
box containing soiled rags and wheat grains ; horsehairs in water
would turn to worms ; and mice and other animals came from the
mud of the river Nile. Dew was supposed to give rise to insects,
and rain would bring frogs. Instead of investigating whether
this was the way life originated, people speculated that it must be
true and scorned anyone who doubted it. The unbelievers were
told to go to the Nile and see the fields swarming with mice begot
from the mud which was deposited when the Nile overflowed its
banks.

Experimental evidence. Francesco Redi, an Italian physician,
(1629-1694), was one of the first persons to conduct a series of
experiments to test, scientifically, the theory of spontaneous

239

240

HOW LIFE BEGAN

mMMMJM»}mmm>MM}m>M»>»m»»wm^»jm

Using this simple experiment, Redi started a discussion which ended
with the overthrow of the belief of spontaneous generation.

generation. He had noticed that flies were usually seen about
meat, and thought that there might be some connection between

flies and the mag-
gots which were
supposed to rise
spontaneously
From the meat.
As a result of
this observation,
he put some meat
in three different
jars. One of
these jars was
left uncovered,
one was covered with parchment, and the third was covered with
a fine gauze. In the first jar, the meat spoiled; maggots and,
later, flies appeared in the mass. In the parchment-covered jar, the
meat putrefied, but no maggots appeared. In the gauze-covered
jar, the meat putrefied, and flies laid eggs upon the gauze. These
eggs produced maggots which later developed into flies. Therefore,
Redi concluded that maggots of flies could not have originated
from decayed meat alone, but from fertile eggs laid there by other
flies that were attracted by the odor. No eggs were found near
the second jar as the parchment kept the odor from escaping.
Redi decided that life must come from preexisting life. He per-
formed other experiments and concluded that in cases when life
seemed to have been produced from dead matter there had always
been the introduction of material from living organisms.

Leeuwenhoek's contribution. After Redi's experiments, the
question of the origin of life was again discussed. Many people
were willing to accept the explanation that the living things they
could see, such as rats and frogs, must originate from other living
things. In 1687, Leeuwenhoek perfected the microscope and dis-

THE IMPORTANCE OF OXYGEN 241

covered an entirely new world of living microorganisms. He dis-
covered bacteria and protozoa, which many investigators said were
the organisms from which more complex organisms originated.
By means of the microscope he was able to prove that the weevils
found in granaries were hatched from minute eggs deposited on
the wheat grains by winged insects.

Needham and Spallanzani. About 1770, Needham, an English-
man, became interested in these experiments. He boiled meat
extract in glass flasks which he closed securely with corks. He
thought he had killed all the life present with the boiling process.
In every case, he found that great numbers of microorganisms
appeared sooner or later. He decided that if life appeared, it
must originate spontaneously. He started the spontaneous gen-
eration controversy anew. The Abbe Spallanzani, an Italian, sus-
pected that Needham had not been very careful in conducting his
experiments and that germs in the air might have entered the flask.
He repeated the same experiments, but used glass flasks that
could be hermetically sealed in a flame while the infusion was still
hot. No organisms appeared. Needham objected to Spallan-
zani's experiment, saying that the prolonged heating had destroyed
the nutritive value of the substance. Spallanzani then per-
mitted some air to enter the glass and almost at once microscopic
organisms appeared, showing that the nutritive qualities of the
material were still there.

The importance of oxygen. About this time a scientist named
Priestley discovered oxygen and its importance to life. Scientists
now asked whether the boiling of the closed flasks had not changed
the oxygen so that it had lost its life-giving properties. But no
more scientific experiments were performed until 1836, when an ex-
periment was devised that permitted clean air to enter the culture
medium continuously. Organisms in the air were removed by
passing the air through a series of tubes containing substance which
would kill all living matter. No organisms appeared in the flask.

242 HOW LIFE BEGAN

Many scientists were now willing to accept the fact that living
organisms did not originate spontaneously.

The revival of the discussion. After some years of practically
no discussion on the subject, Pouchet, in 1859, suddenly revived the
controversy. He believed that spontaneous generation was one
of the means employed by nature for the production of living
things, so he set out to prove it. He filled a bottle with boiling
water and inverted it with the mouth of the bottle under mercury.
Then, by means of a delivery tube, he introduced oxygen through
the mercury into the bottle of water. The oxygen gradually dis-
placed some of the water. By means of a pair of forceps, which
he had first heated, he thrust some hay through the mercury into
the bottle. The hay, too, had been carefully heated to a very high
temperature. The hay floated in the water in the bottle, in the
oxygen atmosphere. Microorganisms appeared in great numbers.

Louis Pasteur enters the controversy. A French scientist,
Louis Pasteur, thought that Pouchet had not set up his experiment
carefully enough and that germs must have entered with the oxygen
or hay. Pouchet asked how it was possible for air to contain so
many germs that they developed in every organic material. He
said the air would be misty with them. Pasteur began to wonder
whether germs might not be more numerous in some air than in
other air.

In order to investigate this, Pasteur filled a number of glass
flasks with a liquid that would easily spoil. He boiled the liquid
and sealed the flasks while the liquid was still boiling. He opened
some of the bottles in different places where there were people
and dust. He then sealed the flasks again, and in all cases organ-
isms appeared. He next went to the Alps to investigate air at an
altitude so high that it would be free from dust. He went to the
Mer de Glace, high up in the Alps. He opened twenty of the
flasks that had been carefully prepared, and immediately sealed
them again. Subsequently, microorganisms appeared in only one

PASTEUR ENTERS THE CONTROVERSY 243

flask. Pasteur concluded that the amount of dust and germs
in different localities must vary. In reporting this experiment
to the French Academy of Sciences, he stated that the study
of the germs which accompanied dust might lead to a knowledge of
the origin of various diseases. But the conception of germs and
disease was so vague that no attention was paid to this statement.

While Pasteur was conducting his experiments in the Alps,
Pouchet was testing air in Sicily, on Mt. Etna, and on the sea. He
found microorganisms in all his air tests. Many people believed
in the validity of Pouchet's work rather than that of Pasteur's.
One scientific journalist wrote that Pasteur's work was too fantastic
to be exact.

Then Pouchet decided to repeat Pasteur's experiment. Accom-
panied by two other scientists, he departed for the Alps with a
number of narrow-necked flasks filled with hay infusion. At the
foot of a glacier of the Maladetta, 3000 meters above the sea level,
he opened four of his flasks. Then the tubes were carefully sealed.
Microorganisms soon appeared in the flasks. Pouchet then con-
cluded, since there was no dust at the place where he had opened
the flasks, that air did not bring in the germs, but that they
must arise by themselves from the organic material.

The debate became so heated that the Academy of Sciences
appointed a commission to examine the experiments of Pasteur
and Pouchet. Both scientists were invited to present their experi-
ments, but Pouchet said the weather was so cold that it might
compromise his results. Some time later, Pasteur was invited to
give a lecture on spontaneous generation at a scientific meeting at
the Sorbonne. A theatrical performance could not have drawn a
larger crowd. Every seat in the room was taken and many
scientists and students were there. Pasteur simply and care-
fully performed his experiments, explained them, and presented
his conclusions. He explained to the audience that boiling
destroyed the germs, but if air entered after the boiling, it carried

244

HOW LIFE BEGAN

in more germs and the organic material would then decompose and
show numerous microorganisms. If care were taken that no
air entered, no organisms appeared. He repeated Pouchet's first
experiment and showed a source of probable error. In a darkened
room, he directed a beam of light upon the apparatus and the
audience saw that the surface of the mercury was covered with
dust particles. Pasteur showed that when the forceps were
plunged through the mercury, they took some of the dust particles
with them. He then explained that the floating particles of dust
contained living germs. Later, the Commission decided that the
contest should be settled by one experiment. Pouchet wanted
more. The Commission refused and gave its decision in favor of
Pasteur.

John Tyndall. In 1876, John Tyndall, an English physicist,
published the results of his experiments. He had devised a very
elaborate box or chamber which enclosed a volume of air. This

was so regulated that any
particles floating in the air
would settle and be held on
a sticky substance, such as
glycerine, spread over the
sides of the box. Tyndall
passed a powerful beam of
light through an opening
in the box to make sure
that no free dust particles
were present in the air. If
dust particles were present
in the air, the beam of
light would illuminate
them. Then he applied heat to the test tubes of nutritive fluids
that were suspended in the box. These fluids consisted of mutton
broth, turnip broth, and fluids from other plants and animals.

Tyndall's apparatus added further data which
helped disprove the theory of spontaneous genera-
tion. Identify the different parts of the apparatus
from the description given in the text.

ORIGIN OF LIFE 245

The mouths of the test tubes were freely exposed to the air in
the box. The fluids remained free from microorganisms for an
indefinite period of time. Later, in order to check his results
and to demonstrate that the fluids contained nutritive value, he
removed them from the box and exposed them to the outside air.
Microorganisms appeared. The importance of this work and the
work of Pasteur was far reaching. Keeping dust out was the
basis for the sterilization of wounds and surgical instruments,
which later led to antiseptic surgery. It was, also, the basis of
canning by heating.

Origin of life. If life comes from life, where did the original
life come from? Science has been unable to solve this riddle.
One theory, popularly accepted by some scientists, is that when
the earth cooled down, there were unusual conditions that made
possible the combining of certain elements in the right proportion
to form the simplest one-celled plants. From these plants, gradu-
ally the entire plant and animal kingdoms have originated. There
are no means of knowing whether this actually took place or not.
The origin of living matter still remains unsolved by scientists.

Questions and Suggestions

1 . State the ancient idea of the origin of life. What evidence have
you for thinking that some people still have this idea about some forms
of life?

2. Describe the first experiment that was made to prove the theory
of spontaneous generation.

3. Discuss the importance played by the microscope in the con-
troversy.

4. Discuss the experiments of Needham and Spallanzani.

5. Of what value to scientists of this time was the discovery of
oxygen ?

G. Discuss the controversy of Pouchet and Pasteur.

7. How do present-day scientists explain the origin of life?

CHAPTER XXVI

ASEXUAL
REPRODUCTION

A moss capsule.

Obelia forming buds.

What is asexual reproduction? What kinds of organisms reproduce
asexuallyf What are some of the asexual methods of reproduction?

Only living things have the power to produce new organisms
similar to themselves. Schleiden, Schwann, and other scientists
showed that cells, living units of life, came only from preexisting
cells. This process of a cell or cells producing other cells is called
reproduction. It is a process peculiar to living organisms. Icicles,
crystals, stalactites, and stalagmites may grow by tiny additions to
the outside. These additions are known as accretions. After
accretion has gone on for some time, parts may break off. This
type of growth and division is fundamentally different from the
growth and division that come from within a living cell. A given
organism cannot live forever; therefore, nature has provided, by
reproduction, a means of continuing the species.

The necessity for division. In living cells, particles of food
material are taken into the cell body and made into cell material,
protoplasm, by the process of assimilation. This additional proto-
plasm causes the cell to grow. The cell grows until it becomes so
large that there is not enough surface to take in Sufficient food for
the increased mass of protoplasm. By the process of dividing in
half, two more surfaces may be obtained, through which food may
be absorbed from the outside. After dividing, each cell again

246

REPRODUCTION BY BINARY FISSION

247

takes in food from the outside, grows to its maximum size, and
then divides again. In the simpler animals and plants, after repro-
duction, the new cells may separate and go about as single individ-
uals or they may cling together. If they cling together, each acts
as a separate individual independent of the other.

Reproduction by binary fission. The simplest of all plant
organisms belong to the Thallophyta. As previously men-
tioned, they are distinguished by the character of having no
division into roots, stems, and leaves. The thallophytes are
divided into two sub-groups: the fungi — thallophytes lacking
chlorophyll, such as bacteria, yeasts, and molds ; and the algae —
those having chlorophyll, such as Pleurococcus and Spirogyra.

Bacteria show little differentiation of structure. They consist
of a mass of protoplasm with nuclear material scattered through
the cytoplasm. They are surrounded by a thin cell wall. Bac-
teria reproduce by splitting in half, thus forming two new indi-
viduals. During reproduction, the nucleus elongates and divides.
A cell wall is formed between the two nuclei, cutting the cell in
half. Probably the division of the nucleus is always a mitotic
division. Sometimes the newly, formed cells remain attached;
often they separate. This type of
reproduction is binary fission.

Many of the algae reproduce
much like bacteria. Pleurococcus
is found on the shady, moist sides
of trees, rocks, and stumps every-
where. Each plant is a single cell
consisting of a cell wall, cytoplasm
and nucleus. It makes its own
food, reaches a maximum size, and
divides. The resulting cells either
separate or remain in clusters.

„. t1 „ ~ . ,. ., , Germs multiply rapidly when conditions

Ihe cells or bpirogyra divide by are favorable.

a.PrfW.

8.30
9.30 _

" "" 8

40-

40.30

11-

G4r

11.30

128

\2JToorL

ZS6

1&30*>K

•SiZ

1024-

8f?M 16.77T.216

248

ASEXUAL REPRODUCTION

binary fission. In Spirogyra, the mitotic figure is clearly seen
when properly stained. As the cells of Spirogyra divide, they

A yeast cell takes in food and grows a bud which enlarges and produces other buds. This
results in a chain or group of yeast cells.

cling together end to end and form a long filament. Each cell
is an independent organism. Amitosis, division without a spireme,
is very infrequent. There is doubt as to Whether amitosis is ever
a method of reproduction in any normal and healthy cell.

Many one-celled animals such as the Protozoa reproduce by
fission. In the amoeba, the nucleus divides mitotically, the
cytoplasm constricts between the two nuclei, and two new cells
are formed. The Paramecium, too, reproduces by a like method.
The micronucleus elongates, constricts, and divides. The
macronucleus resembles a degenerative nucleus in that it divides
amitotically. It frequently disintegrates and dies. Then the
micronucleus builds a new macronucleus. As the cytoplasm
constricts, a new mouth, groove, and gullet appear in one side of
the organism. A new vacuole appears at the end of each new
cell. The cytoplasm divides completely and the two new Para-
mecin swim away from each other.

Reproduction by budding. Another type of reproduction found
among simple organisms is budding.

Problem. Study of budding in yeast cells.

Break a small part of a compressed yeast cake into a dilute solution
of molasses. Stir and then let the mixture stand in a warm place over night.
Mount a drop of the material under the low power and then the high power of
the microscope.

BUDDING OF HYDRA

249

I. Describe the shape, color, and size of yeast cells.

A. Note and describe the large vacuole in each cell.

B. Describe any other structures that you see.

II. Notice tiny protuberances on some of the cells. These are called buds.
This process of reproducing is called budding.

A. Compare the buds with the original cells as to size and appearance.

B. Describe a difference between budding and binary fission.

C. Compare the different buds in size. Account for the difference.

D. Examine the field of the microscope carefully and see whether the
buds always cling to the original cell or whether they separate from it.

E. If the original cell is called the mother cell and the bud is the
daughter cell, do you find any granddaughter cells ? Explain how you
recognize them.

F. There is a nucleus in the yeast cell although it may be difficult to see
it without staining. The nucleus divides mitotically in forming the bud.

G. Draw : 1. Yeast cells ten times larger than seen under the micro-
scope. Label cytoplasm, vacuole, and cell wall. 2. Yeast cells budding.
Label cell and bud. 3. A group of yeast cells' with successive buds.

H. Compare your sketch with the diagram on page 248.

Budding of hydra. Hydra, a small, many-celled animal, is often
seen growing on the side of an aquarium jar. Hydra has a mouth,
several armlike struc-
tures called tentacles,
a thick wall of out-
side body cells, and a
delicate inner layer of
cells inclosing a body
cavity. The tentacles
wave about and cap-
ture food which they
convey to the mouth.
When hydras are
mounted under the

bucL

The hydra often grows a bud and occasionally an animal is
found with a daughter bud bearing active tentacles.

microscope, one or more buds may be seen on the body walls.
Each bud is a new animal in some stage of development.

WH. FITZ. AD. BIO. — 17

250

ASEXUAL REPRODUCTION

Photomicrograph of a hydra.
Note the buds still attached to
the original animal.

Budding is not as common a form of reproduction as binary
fission. Budding and binary fission are types of reproduction
found only among the simplest of plants
and animals.

Reproduction by means of spore forma-
tion. A third type of reproduction found
among simple organisms is spore forma-
tion. If yeast cells are subjected to an
unfavorable condition of heat, food, or
water, they sometimes go through another
type of reproduction. Each yeast cell will
develop an unusually thick wall. The
nucleus and cytoplasm break up into three
to eight parts. Very often only four parts are formed. Each of
these parts is known as a spore. The spores will remain in the
spore case, the thickened cell wall, until the surrounding condi-
tions become favorable for them to live alone. Then the spore
case will absorb water, burst, and the four yeast cells will come
out. Each will feed, grow, and reproduce. This type of propa-
gation accomplishes protection as well as reproduction.

Due to lack of chlorophyll, yeast cells are unable to make their
own food. They depend upon food already made. Their food
consists of fruit juices and other sugar solutions. If molasses
solution, preserved fruit, grape juice, or any
other sweet food is left exposed to the air, wild
yeast plants, in the form of spores, will settle
on the surface and multiply rapidly. The
yeast cells give off enzymes which attack the
sugar, breaking it down into alcohol and car-
bon dioxide. This process of yeast attacking
sugar and converting it into alcohol and carbon
dioxide is known as fermentation. Bubbles of carbon dioxide
may be observed in fermented solutions. The test performed in

<S>

Yeast cells often form
a group of four spores.
These last over an unfa-
vorable period and at the
proper time break from
the spore case. Each
spore becomes a yeast
plant.

REPRODUCTION BY SPORE FORMATION 251

elementary science may be used to show that these bubbles are
carbon dioxide. The alcohol may be recognized by the odor.
The process of fermentation always accompanies the reproduction
of yeast plants. Since the yeasts are dependent upon nonliving
organic material for food, they are called saprophytes.

Problem. Spore formation in mold.

Place a piece of bread on several thicknesses of well-moistened filter paper
or blotting paper on a plate. Expose the bread to the air, sprinkle it with dust,
or infect it with mold spores. Cover with an inverted glass dish that is raised
up on one side to admit a little air. Be sure the bread does not dry. Moisture,
a limited amount of air, warmth, and organic material are necessary for the
growth of molds. The hairy growth that appears on the bread is one type of
mold, the bread mold. It takes from one to four days to grow these plants.

Mount a minute amount of the hairy structure under the low power of the
microscope.

I. Describe the shape and color of the cells of the mold.

A. Are there any cross walls to the cells?

B. Do the cells branch or not? These cells are known as hyphae.

C. The mat of cells is known as the mycelium. The threads that are
actively feeding and growing are called the vegetative hyphae.

II. Try to mount a piece of mold that was actually embedded in the bread.
A. The anchoring rootlike structures are called rhizoids. By means of

these, the mold gives out enzymes that dissolve some of the bread. The
dissolved bread is then absorbed as food by the mold.

I. Observe the structure of the mold and explain why it is prob-
ably a saprophyte.

II. Discuss the difference between the mold and Spirogyra in types
of nutrition ?

III. When the mold is three or four days old, note the tiny dark bodies that
appear. Mount a bit of the mold structure, including several of these bodies,
under the low power of the microscope. Be sure not to take too great a mass
of material.

A. Describe the structure of one of the small black bodies. This is a
sporangium.

B. Describe the structure that holds the sporangium. This is a repro-
ductive hypka.

C. Locate a broken sporangium. Describe the structures escaping

252

ASEXUAL REPRODUCTION

An aerial hypha develops a sporangium or fruiting body.
This structure produces and disperses the spores.

from .the sporangium. These are known as spores. Each little spore is
capable of producing a new mold plant.

D. Draw a complete and a broken sporangium.

I. Label sporangium, spore, and reproductive hypha.

A sporangium some-
times forms at one end
of the hypha. The pro-
toplasm within this end
breaks into a great many
tiny structures, spores.
When ripe, this fruiting
body or spore case, the
sporangium, breaks open
and the spores scatter.
The spores can outlast
unfavorable conditions. During unfavorable conditions, the mold
is in a dormant or resting stage in the spore. If it settles on food
and there are proper conditions of moisture and warmth, then the
spores will develop into new mold plants. The name for some molds
is mildew. Certain of the molds, as the powdery mildew that grows
on the lilac, live and secure their nourishment from living organisms.
An organism that gets nourishment from a living plant or animal,
and gives nothing in return, is a parasite.

Problem. Study of sporangia in various
types of molds.

I. Let a peeled banana stand in a covered dish
for forty-eight hours. When it shows a mold
growth, examine it with the microscope for fruiting
bodies or sporangia.

II. Bring to class samples of various kinds of
molds or mildews. Examine them under the micro- This photomicrograph shows

.,,..,,. . not only a large sporangium,

SCOpe for the fruiting bodies or sporangia. but certain of the spores are

A t-w j.rt. , , » also in focus. Compare this

A. Draw as many different types of spo- illustration ^ the diagram

rangia as you have observed. at the t0 P ot the page.

REPRODUCTION BY SPORE FORMATION

253

II molcl

green
mnol3L

Diff erent species of molds form different types of sporan-
gia. Compare the different sporangia in the picture.

Amoebas and certain
other protozoans may go
into a resting stage simi-
lar to spore formation,
when conditions are un-
favorable. This resting
stage in a protozoan is
called encystment.
Spore formation is not,
necessarily, a method of
reproduction. It may
be a method of protec-
tion only. But since
such a cell can germi-
nate, when brought into
favorable conditions, it
is usually classed with
reproduction. Spallanzani, Pasteur, and Tyndall discovered in
their investigations of spontaneous generation that certain micro-
organisms were harder to kill than others. It was later found
that some are more resistant to a high temperature than others,
and that some are spore formers and can resist unusual condi-
tions, while others are incapable of forming spores.

Each of the types of repro-
duction described, namely binary
fission, budding, and spore forma-
tion, is really a type of cell division.
Each of the new cells formed is
I produced by a single organism.
Therefore, it is called asexual
(without sex) reproduction, in
contrast to sexual reproduction

Certain sponges reproduce by budding. ^ which tWO Organisms take part.

254 ASEXUAL REPRODUCTION

Questions and Suggestions

1. What is the purpose of reproduction?

2. Discuss binary fission.

3. Give examples of organisms that reproduce by binary fission.

4. Discuss reproduction by budding. Illustrate in two organisms.

5. Set up an experiment to illustrate fermentation.

6. Discuss spore-formation in yeast ; in molds.

7. Besides reproduction, what is another purpose of spore forma-
tion?

8. Compare and contrast binary fission, budding, and spore forma-
tion.

9. Compare a saprophyte and a parasite with an organism that
makes its own food. Give examples.

Supplementary Reading

Atkinson, G. F., College Textbook of Botany (Henry Holt & Co.).
Gager, C. S., General Botany (P. Blakiston's Son), chaps, xv-xxv.
Greaves, J. E. and E. O., Elementary Bacteriology (W. B. Saunders), chap. vi.
Holmes, S. J., General Biology (The Macmillan Co.), chap. x.

CHAPTER XXVII

VEGETATIVE
PROPAGATION

Leaf with little plants.

A sandworm with buds.

What is vegetative propagation? What processes in animals may be
comparable to vegetative propagation of plants ?

An individual organism begins its independent life when it
becomes separated from a preexisting individual. Roots, stems,
and even leaves sometimes develop into new plants, although
ordinarily their functions are for purposes of nutrition and not
reproduction. When a portion of a plant, ordinarily used for
nutrition, is separated and used for reproduction, the process is
called vegetative propagation. Vegetative propagation is an asexual
method of reproduction. Usually, only one organism contributes-
to the propagation or continuance of the life of the organism.
Man makes use of vegetative reproduction to produce new species
rapidly. When the method of reproduction of a plant is devised
by man, it is called an artificial method of propagation ; when it
is found in nature, it is called a natural method.

Artificial methods of vegetative propagation. Cuttings. Higher
plants may be propagated by cutting pieces of stems from the
plant and planting these cuttings in moist sand or water. If a
twig is cut from a willow tree, and the cut end placed in water or
moist soil, roots will usually develop from that end, while buds
will develop from the other parts of the cutting. Each cutting will
produce the missing parts and grow into a complete, independent

255

256

VEGETATIVE PROPAGATION

A piece of stem cut from certain plants and placed
in water or moist sand will grow roots.

plant. Geraniums and other house plants are usually propagated
in this way since they may be produced much more quickly from

cuttings or slips than from
the germination of seeds.
Another advantage of slip-
planting is that one is usu-
ally sure to grow a plant true
to the type from which the
slip was taken. The seeds
of plants do not always
develop into plants exactly
like the organisms from
which they were gathered.

Regeneration. • There is a
type of propagation found
among certain animals that
is somewhat similar to cuttings of plants. It is possible for many
organisms to reproduce lost parts and grow into complete individ-
uals. The common earthworm is a good example. If a worm
is cut through the middle, each half may develop the missing parts
and each part may become a complete worm. Certain flat worms
may be divided into several parts and each part will become a
complete individual. Sponges are propagated by cutting a sponge
into many sections and sowing the ocean floor with them. Each
section will develop into a complete organism. The regrowth or
reproduction of the parts of an organism which have been lost or
destroyed is called regeneration. If some animals such as crusta-
ceans (lobsters, crabs, shrimps) and echinoderms (starfishes, sea
urchins, sea cucumbers) lose one of their appendages or rays, they
are able to regenerate these parts. Sometimes a lobster is seen
with one claw much larger than the other. This probably indi-
cates that the smaller is a second growth, the first having been
lost in a fight or through an accident.

STEM GRAFTING

257

In the higher animals, including man, whole organs are not
restored. A process similar to regeneration is evidenced, though,
in the healing of a wound and in the knitting of a broken bone.
An ordinary scratch or even an extensive cut often heals without
so much as a scar, because the destroyed cells are quickly re-
placed by new cells. The capacity of lower animals to regener-
ate an entire individual from a portion of another individual is an
extreme example of the same ability as is manifested in the heal-
ing of a wound. The type of regeneration shown in the regrowth
of destroyed tissues is known as physiological regeneration in con-
trast with the regeneration that is a method of propagation.

Grafting. If, under certain conditions, the freshly cut surfaces
of two plants are brought into contact with each other, the plants
will grow together as one. People for many ages have been using
this knowledge for the propagation of fruit trees. A stem called
a scion is cut from a tree and is so attached to a rooted stem called
the stock that the cambium or growing layers of each are brought
into close contact. The actively growing cambium cells of each
unite the two stems. In time, food from the stock will pass
through the ducts and nourish the scion. This is called astern

/#»

Placnari

Animals often regenerate lost parts. The lower animals, when injured, may grow back
few or many lost organs. The simpler the animal, the greater is the power of regeneration. In
the human body only limited regeneration takes place.

258

VEGETATIVE PROPAGATION

grafting*

graft. During the process of
uniting, the two stems must be
closely bound to prevent them
from breaking apart. A coat of
grafting wax protects the region
of contact from an excessive loss
of sap and evaporation of water,
and from contact with spores of
fungi. Successful grafting is ac-
complished only between mem-
bers of the same or closely
related species. Stem grafting is
commonly used in propagating
fruit trees.

Grafting is, also, done by
means of buds. A bud on a strip
of bark with its underlying cam-
bium layer is cut from a branch
and is inserted into the slit in the bark of the stock so that the two
cambium tissues are in close contact. The process of binding and
waxing is similar to that used in stem grafts. Fruits, nuts, and
flowers are obtained more rapidly by grafting 'than by the plant-
ing of seeds. The graft will probably always breed true to the
scion type. Consequently,
as in the case of propaga-
tion by cuttings, a horticul-
turist is sure of the result of
the graft, if it is successful.
Grafting is also a method of
propagating seedless fruits.
If a seedless fruit has been
produced by plant breeding,
it is propagated vegeta-

eleft grafting

Twigs may be grafted together in
various ways.

+ soion. — * sHieia. bu<wnn

€

Shield budding is a type of grafting. The bud of
the desired variety is inserted into a slit in the bark
of the stock. It is then bound tightly to keep in
place until healing and growth take place.

BUD GRAFTING

259

lively by grafting. Every possible tree of the same or closely
related species may be made use of in grafting. If a tree is found
to produce inferior fruit, instead of uprooting it and planting new
seeds, a scion from a tree that produces good fruit may be grafted
on the inferior tree. If the grafting is successful, the original tree
will, in the future, produce the
improved variety. Varieties of
the Old World grape have been
grafted on the stock of the wild
grape, and from this combination
we have obtained the different
types of grapes found in our
country to-day. The roots of
the Old World grape are easily
injured by a root louse, but
the roots of the wild grape are
not affected by this insect. Be-
sides, the wild grapes are hardy
and are able to grow well in this
climate. By grafting, it has been
possible to produce grape vines
that are immune from destruc-
tion by the louse, and yet yield
the desired type of grape.

A type of grafting is fre-
quently used by surgeons in ani-
mals. But, here, grafting is a type of regeneration and not of re-
production. In most cases, grafting is only used when tissues are
severely injured. For example, if considerable skin has been de-
stroyed by a burn, small sections of skin are removed from other
parts of the body and grafted on the injured area. This grafted skin
grows over the injured area and thus repairs the tissue. If a bone
in the body is tubercular, sections of healthy bone from another

stock

Tongue grafting is a type commonly used.
The important feature here, as in all grafting,
is to bring the cambium layers of stock and
scion together.

260

VEGETATIVE PROPAGATION

Layering is a modification of cutting. It consists in
bending down a stem and covering it with earth. Deep-
notching or ringing the bark of the part buried usually
hastens the rooting of the stem.

part of the organism
may be grafted on to the
diseased bone. But, to
a large extent, grafting
of tissues, bones, and
even organs is still in
an experimental stage
and has not proven suc-
cessful in all instances.
Natural methods of
vegetative propagation.
Layering , another
method of propagation,
often occurs without
the assistance of man.
In many cases the
branches of a tree or

brush may bend down until they come in contact with the soil.

Sometimes they become covered with soil. If there is sufficient

warmth and moisture in the soil, the branches will develop roots.

Frequently, after developing roots, they break off from the tree

and form an entirely new plant. The raspberry, with its arching

stems, illustrates this type

of propagation.

Runners are branches

that trail along the ground.

Sometimes, the ends or

joints of these branches

come in direct contact with

moist soil. Roots and,

finally, a shoot develop at

this point, forming a new

plant. Strawberries, as

r%uvri«r*

-parent.

yoxxnS

When runners are found in plants, they may be used
as an easy and rapid method of propagation.

NATURAL PROPAGATION

261

Underground rootlike stems or rhizomes are charac-
teristic of some plants. As they run under the ground,
they give off buds which form new plants.

well as many grasses and
weeds, are usually propa-
gated in this way. Seeds
of strawberries are so
very difficult to cultivate
that horticulturists de-
pend entirely upon the
runners for propagation.
Rhizome. A common
form of subterranean
stem is the rhizome or
rootstock. It is a hori-
zontal stem running
under the ground. As it grows beneath the soil, it sends off roots
from its under surface, and leaf -bearing branches from its upper
surface. The rhizome is usually somewhat thickened with food.
Growth takes place year after year from the same rootstock which

bears the annual scars of
the ground stems. In the
common ferns, the so-called
fronds are simply large
leaves developed directly
from the rhizome. Blood-
root, Solomon's-seal, wake-
robin, lily of the valley,
and many other spring
flowers are propagated from
rootstocks.

Tubers. The potato
plants have slender, under-
ground stems. Certain

Potatoes can be raised from seeds. The usual . „ .
method of propagating potatoes, however, is to use a reglOllS 01 these Stems en-
part of the tuber with an eye. The eye is a bud | » , « rp,
from which the stems and roots grow. large to torm tubers. lhe

262

VEGETATIVE PROPAGATION

vl.

A whole bulb and the cut section of two bulbs are
shown. Note the short stem and the thick fleshy leaves
arranged around the stem.

" eyes " in the tubers are really buds. When used for propagation,
the potato is cut so that each section has at least one " eye."
These sections can be planted and each bud or "eye " will develop a

root system and an aerial
stem. Each tuber can
form as many plants as
it has buds or "eyes."
Nourishment in the form
of starch is stored in the
tuber and feeds the grow-
ing plant until its leaves
are produced. Some-
times when potatoes are
kept in a damp cellar, the eyes absorb moisture and begin to
develop into stems.

Bulbs. A bulb consists of a modified under-ground stem.
Leaves, thickened with stored foods, grow from this stem and
closely overlap each other to form the scales of the bulb. A
terminal bud growing from the tip of the stem is in the center
of the scalelike leaves. If a bulb is cut, the parts of an entire
plant may be seen. When planted, the embryo stem absorbs
food from the inclosing thickened leaves, sprouts, and develops
into an elongated stem bearing true leaves. As the stem
elongates, it sends up the leaves and flower blossom above the
ground. The true leaves manufacture more food than is needed
and the surplus is sent down to the under-ground stem, where it
is again stored to form another bulb. Sometimes, more than
one bulb will be formed. Onions, tulips, and some lilies are
examples of plants that may be propagated by bulbs. A col-
lection of bulbs may be seen in the narcissus. Bulbs are fre-
quently dug up from the soil so they will not freeze in winter.
Before they are again planted, they are separated from each
other and planted singly.

QUESTIONS 263

In all the forms of propagation discussed, the continuance of
the species is insured. Only one organism is involved in the
process. A part of one organism propagates an entire new organ-
ism. Consequently they are all forms of asexual reproduction.

Questions and Suggestions

1. What is vegetative propagation? Why is it a method of re-
production ?

2. Name three artificial methods of vegetative propagation.

3. Set up an experiment to illustrate propagation by cutting.

4. What is the value of cuttings ?

5. Discuss regeneration.

6. Devise an experiment to show how grafting is done.

7. Name and describe five natural methods of vegetative propa-
gation.

8. Discuss two methods of vegetative propagation by over-ground
stems.

9. Discuss three methods of vegetative propagation by under-
ground stems.

10. Secure, and bring to class, some plants that propagate by
layering, by runners, and by rhizomes.

11. Plant a tuber and a bulb and observe their growth. Draw
them in various stages of growth.

Supplementary Readings

Gager, C. S., General Botany (P. Blakiston's Son & Co.).
Transeau, E. N., General Botany (World Book Co.).

CHAPTER XXVIII

SEXUAL
REPRODUCTION

Maturation of an egg.

Maturation of a sperm.

What is sexf What are some different types of sexual reproduction f

Sexual reproduction in mold. In many organisms, instead of a
single organism developing directly from a half or a part of another
one, two special cells from different organisms unite to form one
cell. The cell resulting from this union develops into a new
organism. The two cells that unite are called gametes, and the
cell formed as a result of the union is called a zygote. The forma-
tion of a zygote is called sexual reproduction. Certain lower plants
reproduce both asexually and sexually. Normally, the bread mold
reproduces by asexual spores. When growth conditions are
unfavorable, a sexual method of reproduction may occur in this
organism. Two threads or hyphae of mold plants will grow
toward each other until the tips meet. A cell wall forms near the
end of each tip, cutting off a part of the protoplasm at the end of
each hypha. These are similar in size and appearance, and are
known as the gametes. The intervening walls between the gametes
are dissolved and the contents of the two cells intermingle. A
thick wall develops around the fused material, the zygote. As the
zygote grows the outer wall becomes black. The structure in this
stage is called a zygospore. Under favorable conditions the zygote
germinates, and develops into a new plant.

When the uniting gametes of an organism are* very similar in
size and activity, their union is -called conjugation. Therefore, a

264

SEXUAL REPRODUCTION IN SPIROGYRA

2G5

zygospore may be defined as a structure resulting from the conju-
gation of similar gametes. Although the hyphae of a mold all look
somewhat alike, there must be a physiological or cjiemical differ-
ence between them. It has been
observed that there are two
types of hyphae, which have
been named the plus and the
minus strains. If a plus strain
meets a minus strain, conju-
gation will occur. It is now
possible to isolate or to pur-
chase plus and minus strains
of mold spores. When these
are planted on opposite sides
of a slice of moistened bread,
hyphae will grow out from each
strain and when they meet,
zygospores are formed.

Sexual reproduction in Spiro-
gyra. During sexual reproduc-
tion in the Spirogyra, portions
of the cell walls between the
two filaments grow perpendic-
ular projections and form a
bridge. The cell walls in the
middle of the bridge are dis-
solved, probably by the action
of enzymes. Then through the
work of vacuoles the entire contents of the cell in one filament are
moved across the bridge and fused with the protoplasm of the
other cell. After conjugation, a thick cell wall develops around
the fused protoplasm and the structure is known as a zygospore.
If one cell in a filament is an active cell, that is, its contents^ pass

WH. FITZ. AD. BIO. — 18

..Zygospore

Hyphae of mold plants grow toward each
other and meet. In the area of contact, mate-
rial from each intermingle to form a zygospore.

266

SEXUAL REPRODUCTION

ROl^l

through the bridge, all
the cells in that fila-
ment are active cells.
If one individual in a
filament is a passive
cell, all other cells of
that filament are pas-
sive or receiving cells.
There is more physio-
logical differentiation
in the Spirogyra than
in the mold, in that
the gametes behave
differently. The ac-
tive gametes may be
compared to male gam-
etes of higher plants and animals, the passive, or receiving gam-
etes, to female gametes. After the zygospores are formed, the
filament sheath breaks down, the cell walls disintegrate, and the
zygospores fall to the bottom of the pond. They stay in a dor-
mant condition until there is sufficient water and warmth to pro-

There seems to be two different strains of bread mold
called plus and minus. The hypha of unlike strains attract
each other and zygospores are formed.

When two threads of Spirogyra lie parallel to each other, ad-
jacent cells may send out little tubes which meet. The cross
walls in the tubes become dissolved, leaving an unobstructed
bridge. The entire contents of one cell (active gamete) will pass
over and mingle with the contents of the other cell (passive gam-
ete). Fusion takes place and a zygospore is formed. If one cell

in a filament has a moving gamete, the contents of all the cells of that filament behave in

a similar way.

REPRODUCTION IN PARAMECIUM

267

Each of the cells which fuse during conjugation is
known as a gamete. When very nearly alike they are
called isogametes. Conjugation is the result of the
fusion of part or all of the cell contents of isogametes.
The result of the union is a zygospore. /

mote their germination. Then each zygospore absorbs water,
breaks the zygospore case, and forms a new filament as a result
of binary fission. There like or isogojnetes
is enough stored food in
the zygospore to start the
germination and sustain
life until the filament can
make its own food.

Sexual reproduction in
Paramecium. Paramecia
ordinarily reproduce asex-

ually by binary fission. Occasionally, sexual reproduction takes
place. Two cells lie next to and in contact with each other.
At the point of contact the cell membranes dissolve. Various
complicated changes take place in the nuclei of the two animals.
The macronucleus in each breaks up and disintegrates. The
micronuclei go through a number of divisions and finally one
fragment of each micronucleus passes over and unites with a
fragment of the micronucleus in the opposite cell. After this
mutual exchange and fusion of micronuclear material, the two
Paramecia separate, and the micronucleus
of each goes through further complicated
divisions, which result in the formation of
both a micronucleus and a macronucleus.
The conjugation of the Paramecia seems
to bring about a renewed vigor. In cer-
tain species conjugation may occur once in
every two or three hundred generations,

a photomicrograph showing although these same species may live a very
the conjugation of Paramecia. i ong timej providing conditions are favor-
able, without ever reproducing sexually.

Certain recent experiments have shown that the environment
affects the vitality of the Paramecium. By removing wastes and

268

SEXUAL REPRODUCTION

The photomicrograph of a mold culture
which shows several zygospores.

by keeping proper food present, thousands of generations have
been produced from a single healthy individual of a certain species.

Under these conditions, conjuga-
tion has not taken place between
any two animals, but certain in-
ternal changes occurred which
were observed and described.

Sexual reproduction in higher
plants and animals. In the sexual
method of reproduction of the
Spirogyra, the entire cell acts as
the gamete. In the Paramecium,
simply a part of the micronucleus
acts as the gamete, but like-sized
portions of the micronucleus unite. When gametes are similar they
are known as isogametes or like gametes. In most higher plants
and animals, certain specialized organs produce cells that form
gametes. There are two kinds of gametes. One, a very small
cell usually equipped with a motile tail, is called the microgam-
ete or the sperm cell. The other type of reproductive cell is the
receiving or passive cell. It is larger and is
called the macrogamete or egg. It usually
stores food particles called yolk granules.
When the egg is ripe, a sperm may penetrate
the egg. The nucleus of the sperm fuses
with the nucleus of the egg. This process
is called fertilization. The cell formed by
the union of the egg and sperm cell is
known as a zygote.

Maturation. Every species of an organ-
ism has a constant number of chromosomes.
The number is always the same for that species. During fertili-
zation, when two cells unite, the number of chromosomes would

Photomicrograph of filaments
of Spirogyra showing conjuga-
tion and zygospores.

MATURATION

269

egg + ®perm * fertile egg
macrogoroetef microganKfce,* wgbte,

Fertilization is the union of dissimilar gametes ;
the union results in a zygote or a fertilized egg.

double were it not for certain changes which occur in the de-
velopment of the egg and sperm. These changes are called mat-
uration or the ripening of tlie
gametes. The cells that are to
produce the germ cells or gam-
etes are the primary sex cells.
They have the same number of
chromosomes as the somatic or
body cells. When ready to ma-
ture, the sex cells split by a process much like mitosis, but the chro-
mosomes do not split lengthwise. Instead of splitting evenly,
one half the total number of unsplit chromosomes goes into one
daughter cell and one half goes into the other. This is the part
of the ripening or maturation process called reduction division.

The number of chromo-
somes is reduced one
half. After this, each of
these cells again divides,
mitotically. Thus from
every primary sex cell,
cells are produced, each
of which has • half the
original number of chro-
mosomes. If» the pri-
mary sex cell had eight
chromosomes, each
gamete would have half
this number or four chro-
mosomes. The produc-
tion of the sperms by
maturation of the pri-
mary sex cells is called
spermatogenesis ; the

reBAxetion.

$'&$&

-„ The primary sex cells of the fruit fly have eight chro-
mosomes. During the ripening process, reduction divi-
sion takes place; the resulting cells have one half the
original number, in this case four chromosomes. Each
of these cells then divides, mitotically forming the sex
cells. From each primary male sex cell there forms four
sperms, all of which can function. Each primary female
sex cell gives rise to one egg and three reduced cells
known as polar cells. The egg has most of the yolk and
is generally the only one of the female sex cells to function
as a gamete. One sperm unites with a mature egg in the
process of fertilization.

270 SEXUAL REPRODUCTION

production of the mature eggs is called oogenesis. All of the
spermatozoons or sperms of a species are of the same size and
structure. All may function. Each of them has a tail-like
structure of cytoplasm called the flagellum. By means of the fla-

gellum the sperms are
able to move about.
Oogenesis is essentially
the same as spermato-

Many sperms of animals may swim about the mature egg. o>pnp«ji«i Onp la rap ppII

One sperm penetrates the cell membrane of the egg and 5 C11CS1 °- vuciaigctcii

carries, in this case, four chromosomes. These are added jg ^g real functioning

to the reduced number in the nucleus of the mature egg. &

The union of sperm and egg with the restoring of the original gamete, Called the ma-
number of eight chromosomes is fertilization.

ture egg. It contains
the food supply or yolk. In the process of maturation of the egg,
three minute cells known as polar bodies are thrown off.

Fertilization. After the maturation process, the gametes
formed from the primary sex cells are ready for union or fertiliza-
tion. The sperm is always in a moist environment and by means
of its flagellum swims to the egg. In some eggs there is a small
opening in the membrane called the micropyle. Through this
opening one sperm enters. When an egg lacks the micropyle, a
sperm penetrates the plasma membrane. The head of the sperm
contains the nucleus. The flagellum or tail of the sperm is usually
left outside of the egg. After a sperm nucleus enters the egg, a
chemical change takes place within the cell membrane. This
permanently seals the egg so that no more sperms can enter.
The nucleus of the egg and of the sperm fuse. The entrance of
the sperm restores the original number of chromosomes in the
egg cell. Mitosis of the fertilized egg then takes place. It differs
from typical mitosis in that half the number of chromosomes
came from the sperm and half came from the egg. The chromo-
somes are said to be paternal and maternal in origin. Immediately,
mitotic division or cleavage takes place and two cells are formed,
each with the same number of chromosomes, as the species

PARTHENOGENESIS

271

to which the parents be-
longed. From here on the
cells cleave or split again
and again by mitosis until
enough cells are formed to
take on the shape of the
plant or animal embryo.
The yolk in the egg sup-
plies food for the rapidly
dividing cells. Fertiliza-
tion produces a variety of
characters by combining
chromosomes from differ-
ent individuals. This re-

Spring and summer aphids or plant
lice are wingless females which pro-
duce young, parthenogenetically, e very
10 to 20 days. In the autumn, males
are produced, mating occurs, and fer-
tilized eggs are laid which last over the
winter and hatch into females the fol-
lowing spring.

The parthenogenetic frogs produced experimentally
hy Jacques Loeb resembled normal frogs in their ap-
pearance.

suits in the possibility of slight or great
differences among offspring.

Parthenogenesis. It has been stated
that the entrance of. a sperm into an
egg stimulates a chemical change in the
membrane which seals the micropyle,
and stimulates the egg to go through
repeated divisions. The late Jacques
Loeb, formerly at the Rockefeller Insti-
tute, carried on a series of experiments
to investigate the nature of the fertili-
zation process. He pricked the eggs
of sea urchins with an electric needle
and found that this brought about a
membrane activity and the egg began
to cleave. He next found that certain
chemicals caused the same results.
This process of the development of the
egg without the entrance of a sperm

272 SEXUAL REPRODUCTION

is known as parthenogenesis. Loeb succeeded in developing, par-
thenogenetically, frogs' eggs. Several reached the tadpole stage.
A few grew to be nearly adult in appearance and then died.
Their development was incomplete. Parthenogenetically devel-
oped organisms may have only half the number of chromosomes
common to the species, since no sperm chromosomes are present.
The process has never been performed, experimentally, in any
organism higher than the frog. It sometimes occurs in nature
in certain of the insects and certain worms.

Questions and Suggestions

1. What is the difference between sexual and asexual reproduc-
tion?

2. Discuss sexual reproduction in the mold ; in the Spirogyra.

3. State a difference between conjugation in mold and Spirogyra.

4. Discuss sexual reproduction in Paramecium.

5. What is the value of sexual reproduction in the life history of
the Paramecium.

6. Compare fertilization with conjugation.

7. Discuss spermatogenesis ; oogenesis.

8. What is the purpose of maturation ?

9. State two cellular activities of the egg that always follow the
entrance of sperm.

10. State two differences between an unfertilized and a fertilized
egg.

1 1 . What is parthenogenesis ? Discuss some experiments that have
been carried on in parthenogenesis.

Supplementary Reading

Atkinson, G. F., A College Textbook of Botany (Henry Holt& Co.). *

Gager, C. S., General Botany (P. Blakiston's Son & Co.).

Holmes, S. J., Ah Introduction to General Biology (Harcourt, Brace & Co.).

CHAPTER XXIX

REPRODUCTION

OF HIGHER

PLANTS

Insect pollination.

Wind pollination.

How are new plants formed? What is the function of a seed and
of the fruit f What are some different types of fruits f

A flowering plant consists of the nutritive organs, the roots,
stems and leaves, and the reproductive organs, which are found
in the flower. The reproductive organs in the flower produce
specialized cells, gametes, which function in sexual reproduction.

Problem.' Study of the tulip.

If the tulip is not in season, the gladiolus, sedum, or any perfect flower may-
be used. (The flower was probably studied in elementary science, so certain
facts learned at that time are not emphasized in this exercise.)

I. Remove the three outer sepals and the three petals found within them.

A. What is the relation of the position of these parts to the organs found
in the center of the flower ?

B. What are the functions of the sepals and petals?

II. Locate the organs in the center of the flower. Why are they called
essential organs ?

A. The single enlarged structure found in the center of the flower is the
pistil. The upper end comprises the stigma. The lower part of the
swollen stalk is the ovary.

B. The structures with spear-shaped heads arranged around the pistil
are the stamens. The heads of the stamens, the anthers, produce the pollen.
How does the pollen escape from the anthers ?

C. Draw a pistil. Label stigma and ovary. Draw a stamen. Label
anther and pollen.

273

274

REPRODUCTION OF HIGHER PLANTS

III. Shake some pollen from the anther on to a glass slide. Mount under
the microscope.

A. How many cells make up each pollen grain?
'■ ... B. Describe the shape, color, and structure of pollen.

C. Draw and label several pollen grains enlarged ten times.

IV. Cut a thin cross section of the ovary of the pistil. Examine it with a
hand lens.

A. The seedlike structures are the ovules. Note that the ovules are
attached to the ovary wall and are not loose in the ovary. The part of
the ovary wall to which the ovules are attached is called the placenta.

V. Place an ovule on a glass slide. Cover it with a cover glass and crush it
by carefully pressing down with the cover glass.

A . Does an ovule consist of one or more cells ?

B. Note a central structure. This is the embryo sac containing the egg
cell.

C. Draw the outline of an ovule showing the position of the embryo
sac.

Structure of the flower. The flower consists of a calyx made up
of sepals and a corolla made up of petals. While the essential

organs are ripen^
ing, they are pro-
tected from rain,
insects, and certain
mechanical injuries
by the tightly en-
folding calyx and
corolla. The whole
structure com-
prises the bud. As
the essential organs
ripen, the calyx
and corolla unfold

The essential organs for the reproduction of higher plants are the
stamens and pistils. Accessory organs are the sepals and petals, and expose the
The sepals enfold the entire flower, forming a bud. Thus the .

organs are protected while they are ripening. The petals are fre- matured pistils and
quently showy and attract insects. This may result in pollination.
The stamens produce pollen and the pistil produces ovules. Stamens.

petal

Stamen.

PRODUCTION OF THE MALE GAMETE

275

Problem. What effect has a sugar solution on
pollen grains t

Make up cane sugar solutions of thirty-five per cent,
ten per cent, and three per cent. Take three hanging-
drop glass slides and on each one lay a cover glass from
the center of which hangs a drop of sugar solution con-,
taining some pollen. Use a different sugar solution for
each slide. Seal the cover slip air tight by means of
vaseline. (Petri dishes or Syracuse watch crystals may,
also, be used.) Different pollen requires different
concentrations of sugar solution in order to grow. A
three-per-cent sugar solution is usually needed for tulip,
narcissus, and onion ; fifteen per cent for sweet pea and
nasturtium. Let the preparations stand for one or two
days. Then mount under the microscope.

I. Describe the shape of the pollen grains when first
produced by the anther.

II. Describe what has happened to the grains.
A. These outgrowths are called pollen tubes.

^ B. Describe the food for the pollen tubes which
you have grown.

III. Carefully crush the tip of a ripe stigma on a
glass slide and mount under the microscope.

A. Do you find any pollen grains here?
1. How did they get on the stigma?

B. Do any pollen grains show pollen tubes ?

1. In which direction are they growing?

2. Where must the germinating pollen tubes
obtain their food ?

IV. Draw and label a germinating pollen grain.

itube
nucleus

Production of the male gamete. Pollen is
produced in the anther of the stamen. Certain
cells in the anther go through a maturing
process in which reduction division takes place.
Mature pollen nuclei contain one half the number of chromosomes
characteristic of the other cells of that particular plant. When

A pollen grain has two
nuclei, one a tube nu-
cleus, the other a gener-
ative nucleus. As the
pollen grain forms the
pollen tube, male gam-
etes (the sperm nuclei)
are produced from the
generative nucleus.

276

REPRODUCTION OF HIGHER PLANTS

mature, the ripe anther of the stamen splits and scatters the
pollen. Agencies, such as wind, insects, or water, may assist in

Complicated nuclear divisions in the embryo sac of the ovule of a plant result in the formation
of eight nuclei, of which one is an egg nucleus and two are polar nuclei. The two polar nuclei lie
near the center of the cell. The egg nucleus is the female gamete.

scattering the pollen. When pollen reaches the stigma of the
pistil, it may be caught and held by hairy outgrowths particularly
adapted for that purpose. The stigma then secretes certain
nutrient materials which the pollen absorbs. After this pollina-
tion*, the pollen grain germinates by sending out a slender thread-
like tube. The pollen tube
grows down through the pistil
and penetrates the ovule
through an opening called the
micropyle. As it grows, cer-
tain nuclear divisions take
place, which produce two sperm
nuclei. The sperm nuclei with
their reduced number of chro-
mosomes are the male gametes
of the plant.
* Production of the female

A photomicrograph of a part of an ovule show- -n i_ 1 j.i~

ing the nuclei in the embryo sac. Compare it gamete. J^aCIl OVUie in the
with the diagram at the top of the page. » j , i_

ovary is lormed as the out-
growth of a few cells from the ovary wall. One of the cells in
the interior of the young ovule appears larger and richer in

FERTILIZATION

277

protoplasm than the other cells. It divides, and, in the division,
reduces the number of chromosomes by one half. There are a
number of complicated divisions that follow. Ultimately, an egg

£ermmatinc£
& poller &

anther

amcri

ovcit

r e g£ cell

A longitudinal section of a pistil shows pollen grains germinating through the pistil in the form
of tubes. One tube is shown penetrating the micropyle of the ovule. The pollen tubes carries
the sperm cells to the embryo sac of the ovule.

nucleus and two polar nuclei are produced among other nuclei
found in the embryo sac. The egg nucleus with its reduced
number of chromosomes is the female gamete of the plant.

Fertilization. When the end of the pollen tube gets to the
embryo sac, the wall of the pollen tube and the wall of the
embryo sac are dissolved and one of the two sperm nuclei unites
with the egg cell nucleus. The two polar nuclei fuse and the
second sperm nucleus sometimes unites with them. This completes

278

REPRODUCTION OF HIGHER PLANTS

m*cl«u* "\ xy6 ote

In the process of fertilization in a flower a
sperm nucleus unites with an egg cell nucleus
to form the embryo of the future plant. The
other sperm nucleus unites with a pair of
nuclei, the polar nuclei. This latter union re-
sults in the endosperm nucleus which divides
and, in time, forms the food supply for the
embryo. Double fertilization is characteristic
of flowering plants.

the process of fertilization. The
union of the sperm and egg nu-
clei forms the one-celled embryo
which develops into a tiny
plant. The union of the other
sperm nucleus and the polar
nuclei forms the cell that starts
the endosperm which is the food
supply of the tiny plant. This
double fertilization results in the
future plant and its food supply.
Formation of the seed and
fruit. There are ducts going
from the plant through the

.remains of stigma
ana ♦st^-Ie^-

.....placenta:

placenta of the ovary to the ovule.

Food passes through these ducts, *

which nourishes, and effects the I

rapid division or cleavage of cells I

in the tiny embryo in the ovule. 1

At the same time, the endosperm \
tissue of the ovule grows rapidly and
stores the future food supply for the
embryo. As the embryo develops

into a many-celled structure, dif- :

ferentiation of the cells sets in and |

the first root or hvvOCOtyL the first After fertilization takes place in a

J vr v > J flower, the petals, stamens, and frequently

bud Or plumule, and the Seed leaves * h e stigmas of the pistil dry and generally

fall off. The embryo and endosperm de-

Or Cotyledons are formed. The en- veloo and the ovule coats grow to accom-

, ii i • modate the increased size of the seeds,

dosperm develops at the Same time, The pod with its contents is the fruit.

hypoccfc>d

FORMATION OF THE SEED AND FRUIT

279

■jrr

In the grains, the endosperm is a well-developed, localized, and
easily identified structure ; in seeds such as beans, peas, and many
nuts, the cotyledons possess
the food supply for the devel-
oping plant.

While the embryo and endo-
sperm are developing, the ovule
coats absorb food from the
ducts and develop into seed
coats. The ripened ovule and
its contents constitute the seed.
The ovary wall grows to accom-
modate the developing seeds
and forms the fruit. The fruit
protects the seeds until they
are completely developed.
Fruits are frequently adapted
to disperse the ripe seeds.
These seeds escape from the
fruit, and the embryos they con-
tain will develop into new
plants, if they fall on moist
soil of proper temperature.
The fruit is a ripened ovary and its contents, together with any
other part of the plant that has ripened with it.

When the bean seed is planted, it absorbs water, and sends a
little arched shoot, the hypocotyl, into the ground. The lower
seed or radicle forms the root system. As the upper part or
true hypocotyl straightens out, it brings the plumule above the
ground. This forms the stem and leaves. The cotyledons feed
the tiny plant until its leaves are able to make sufficient food to
carry on the life process. The cotyledons may either remain under-
ground or be lifted into the air by the growth of the hypocotyl.

Given the proper conditions of moisture and
warmth, a new plant will develop from the embryo
in the seed. Which of the organs of the plants is
developed from the hypocotyl ?

280 REPRODUCTION OF HIGHER PLANTS

Questions and Suggestions

1. Name the parts of a flower and give the function of each.

2. What do we mean by self- and cross-pollination ? What are
some agents of' cross-pollination ?

3. Will the pollen of a daisy germinate on a rose ? How do you
know?

4. Give the history of the pollen grain from the time it is pro-
duced until it functions.

5. Give the history of an ovule until fertilization takes place.

6. Discuss the fertilization of an ovule.

7. , How many seeds can possibly be produced in any plant ?

8. What three processes are necessary for the formation of- a seed ?

9. Discuss the development of a seed and a fruit.

10. Discuss the adaptations of the following plants for dispersing
their seeds : maple, elm, thistle, Bidens, pea, apple.

11. Give examples of seeds or fruits dispersed by (a) wind;
(6) animals.

12. Cut a longitudinal section of some fruit (apple, cucumber, water-
melon, pea). Draw and label seed, seed stalk, placenta, ovary wall.

13. Plant a bean seed. When it appears above ground, uproot it
and draw. Label hypocotyl, plumule, and cotyledons.

CHAPTER XXX

REPRODUCTION
OF ANIMALS

N. Y. Zoological Soc.
The buck has antlers.

N. Y. Zo'dlogical Soc.
A doe with her fawn.

7* the reproduction of an animal similar to that of a plant f Do all
animals reproduce in the same way? IJow does an animal develop
from the fertilized egg f How long does the development take f

Seeds and eggs. The common form of propagation for higher
plants is through the formation of seeds, and for higher animals,
through the production of fertile eggs. Most seeds are capable of
sprouting even after remaining at rest for a long time, sometimes
after many years. The germs in the seeds are destroyed, how-
ever, if the seeds become very wet and then dry again.

The eggs of chickens and other birds are well known. The eggs
of fish and frogs are somewhat similar to those of birds, although
they are found in the water. Eggs of butterflies may frequently
be seen on plants. Those of water animals usually die if they
become dry. Birds' eggs have to be kept warm if they are to in-
cubate and to hatch. Those of insects may lie dormant over the
winter and develop in the spring. In general, eggs need more care
than seeds. In the case of many animals, the eggs must develop
soon after they are formed or they will die. They cannot live in
a dormant form for an indeterminate period of time as seeds can.

Secondary sexual characters. In the lowest animals, it is often
quite impossible to distinguish the individuals that produce male

WH. FITZ. AD. BIO. — 19 281

282

REPRODUCTION OF ANIMALS

gametes from those that produce female gametes. Among the
frogs, fishes, and other lower animals, there is little external mor-
phological difference in sex, but the higher species of animals show
external differences. In addition to the structures that are directly
related to producing and discharging gametes, distinct character-
istics are found in other parts of the body. The males of many
species of birds can be easily recognized by the crests on the heads
and spurs on the legs. The male birds are usually more gayly
colored and have sweeter songs than the female birds.

Among many mammals (animals that are warm-blooded,
covered with hair, and suckle their young), there are usually differ-
ences in horns, size of body, habits, voice, temperament, and in-
terests. Contrast the male reindeer with the doe. The male is a
huge animal with tremendously large antlers. He is a vicious
fighter and protects the doe. She lacks antlers, is proportion-
ately small and slender, and usually depends upon the male for
protection. The differences just noted are called the secondary
sexual characters of reindeers.

Spawning of frogs. Fertilization takes place in animals in a
way very similar to plants. The gametes mature and are then
brought together in a way peculiar to the organism. Different

The lioness and lion show interesting secondary sexual characters.

shaggy mane of the lion.

N. Y. ZoOiogicul Soc.
Note the huge head and

SPAWNING OF FROGS

283

species of frogs reach
maturity in different
periods of time. At
maturity, the female
frog lays fifty or a
hundred eggs,, ova, in
the water. Each ovum
consists of a tiny cell
surrounded by yolk or
food which is covered
with a gelatinous
coating. The adult
male frog discharges
sperms into the water.
These sperms are mo-
tile, swimming by
means of tiny tails.
If a sperm comes in
contact with an egg,

it penetrates the egg The cow, placid in disposition, is easily distinguished from

the excitable and frequently dangerous bull.

membrane, and the

nuclei of the egg and sperm unite in the fertilization process. If the
eggs are not fertilized, they soon die and disintegrate. If sperms
do not reach eggs, they, too, are wasted. The fertilization of
the frog's eggs is external to the body and takes place in the
water. This differs from the plant where fertilization was in-
ternal, taking place in the ovary of the pistil. After fertilization,
the gelatinous sheaths of the frog's eggs absorb water and swell.
This mass of foamy material insures some degree of protection
against enemies. Fish or other frogs cannot readily swallow this
huge mass of gelatinous eggs.

Fish spawn in a way very similar to frogs. They usually go to
quiet, shallow waters for spawning, although a few species of

284

REPRODUCTION OF ANIMALS

I Q.-he«a,
" nucleus

-tail.
wtoplasJ

Fish seldom show secondary sex characters.
The sex organs are the ovaries in the female, and
the testes in the male. The ovary produces nu-
merous ova, each of which contains a yolk and a
nucleus. The testis produces numerous sperms,
each of which has a nucleus, a head, and a
motile tail.

river fish spawn in the ocean. So powerful is the urge to spawn
in natural spawning grounds, that the salmons will leap falls or
artificial barriers in their efforts to reach quiet water on their way
from the deep sea. Many die of exhaustion on their way if they
meet too many obstacles. Those that surmount the barriers usu-
ally die soon after spawning.

Production of eggs. Certain organs of the frog are specialized
for the production of gametes. In the female, the two ovaries
secrete hundreds of tiny ova. The ovaries may be compared to
the ovaries or pistils of flowers which produce egg cells. Ovaries
are common to all females in the animal kingdom. The ova of
the frog go through a maturation process in which the number of
chromosomes is reduced one half. This process results in the
production of mature gametes. The mature ova reach the body
cavity of the frog and then pass through the tubes called oviducts
into the cloaca. They leave the cloaca by means of an open-
ing at the posterior end of the female frog's body and pass into
the surrounding water. Ova are characterized by their compara-

PRODUCTION OF SPERMS

285

tively large size, due to the yolk in them, and the fact that they
are incapable of independent motion.

Production of sperms. The pair of organs that secretes the
male gametes or sperms is the testes. The sperms, too, in the
maturation process lose half their chromosomes. By means of
tubes the mature sperms of the frog pass from the testes into the
cloaca and out of the body. These sperms are known as milt.
Each sperm is a single cell consisting largely of a nucleus. The
cytoplasm is drawn out to form a tail. By means of the tail
lashing back and forward, the sperm swims in the water. (Prob-
ably a chemical attraction draws the sperm to the egg.) The
nuclei of the sperm and egg fuse in the fertilization process, form-
ing a fertilized egg cell, the one-celled embryo. In this process
the original number of chromosomes is restored.

The entrance of the sperm into the egg effects the initial devel-
opment of the egg as well as brings about variation by combining
the chromosomes from two parents. * Each fertilized egg contains
one-half maternal and one-half paternal chromosomes.

Development of the frog. The fertilized egg or embryo absorbs
food from the yolk. It grows and divides mitotically to form a
two-celled stage. These
two cells feed, grow, !$¥&*•

and divide to form a sy

jour-celled stage. Mi- //

totic divisions con-
tinue, forming various
many-celled stages
called cleavage stages.
Finally, the solid mass

Ot Cells, the morula, p rimaryse xcells are formed early in the life of an organism,

becomes arranged in They contain the same number of chromosomes, 2x, as body

& t cells. In the maturing of the sex cells to form sperms and

the form of a single- eggs, the chromosomes become reduced to half the number,

f x. When the sperm unites with the egg to form the zygote,

layered hollow ball of the 2x number is again restored.

286

REPRODUCTION OF ANIMALS

cells known as the blastula. The blastula pushes in just as a rubber
ball may be dented in by pushing on one side. A double-layered,

fertile egg 2-celIecL -4-celIeU

,eleccvacf€
.cavity-'

primitive

Jut

la cellecl
embryo

TiolWixxlI-
blastula

beginning
of gastrula

8ncelIe3L
ectoclermv

l<$-cellea
en^Locterm.

—mouth

two layered
gecs-tr-ulcc

The embryo begins as a single fertilized egg. This divides to form two, then four, and cleav-
age continues until a great many cells are formed. Gradually differentiation sets in and special-
ized structures may be recognized. Thus the various organs of the organism develop.

cup-shaped structure known as the gastrula is thus formed. The
embryo is now two-layered. The outer layer is the ectoderm, the in-
ner layer the endoderm. A mid-
dle layer, the mesoderm, soon

sperm

fertile eg£

cleavage

blastxxla

4
gbcst-rulcc

/ | V

ectdcLerm mesoderm endoderm,
epidermis muscles a.i£estiv<,

central excretory ,r- A

nervous oy^tieni/ «ver ana.
system ^ nccas Pancreas

Skeleton

The fertile egg, by repeated divisions and certain
changes, becomes the gastrula with its three pri-
mary germ layers. Further differentiation and de-
velopment goes on and the organ systems arise.

appears between the ectoderm
and the endoderm. The folded
edges of the gastrula grow
toward each other, forming a
tiny mouth. Marked differ-
entiation now starts and forms
the characteristic tadpole.
The skin and nervous system
are formed from the ectoderm.
The digestive and respiratory
systems are formed from the
endoderm. The excretory, re-
productive, muscular, skeletal,
and blood systems form from the mesoderm. During this develop-
ment the yolk is entirely absorbed by the actively dividing cells-

LIFE HISTORY OF THE FROG

287

Life history of the frog. The little tadpole then hatches from
the gelatinous egg. For the first two or, three days, it remains
attached to grass by
a sucker-like mouth.
Then it begins to
feed on algae and
other vegetable
matter. When first
hatched, it has ex-
ternal gills, which
grow out into long,
branching tufts.
Later, four pairs of
internal gills are
formed and the ex-
ternal gills are ab-
sorbed. The hind
limbs soon appear ;
later, the fore limbs
develop. The tail
then decreases in size
and is gradually ab-
sorbed. The gills,
too, are absorbed,
and lungs are formed
to take their place.
The two-chambered
heart of the tadpole becomes the three-chambered heart of the frog.
Finally the form resembling that of the adult frog is acquired.

Reproduction of other animals. The reproduction of all higher
animals is similar to the reproduction of the frog. All females
have ovaries producing eggs, and males have spermaries or testes
producing sperms. The sperms fertilize the eggs and thereby

N. Y. Zoological Soc.
The frog first hatches from the egg in the form of a tadpole.
Gradual changes take place which transform it into the adult
frog. This change of body form is called metamorphosis.

288

REPRODUCTION OF ANIMALS

cause the formation of embryos. Sperm cells must be kept moist
in order to function. In the case of frogs and fish, fertilization is

external and the water keeps the cells
moist. In the case of animals that do
not live in the water, such as insects,
birds, or mammals, the egg cell is re-
tained within the body of the female,
and the union of the egg and sperm is
internal. Thus the danger of the gam-
etes drying is averted. The embryo
develops outside of the body when the
fertilization is external. The water
also keeps the developing embryo
moist. When the fertilization is inter-
nal, the embryo may partially develop
or may completely develop within the
body of the female. For example, the
eggs of the insects start developing
within the female, but later they are de-
posited in the ground or on plants and
the development continues there.

Amer. Museum of Natural History r

In the birds, the original egg cell ^^___ __^^ ^Vl©ll

and yolk become surrounded by
other materials during the passage
down the oviduct. It becomes sur-
rounded by a coating of albumen,
the white of the egg, which is se-
creted by the glands of the oviduct.
A lime coating which forms the shell
is then secreted around the whole

In the case of birds,

membrane,

A section through a chicken's egg shows the tmy em-

the embryo Starts an in- bryo attached to the yolk. Surrounding the yolk is the

, , , albumen which protects the embryo from shock. Two

temal development, thin membranes within the shell form an air chamber at

The fertilized egg re- oneemL

ceives a huge deposit of yolk, then albumen is spread around it,

and finally it is enveloped in a hard shell of lime. The yolk

REPRODUCTION OF HIGHER ANIMALS

289

"brotin
-heart

£l£e ©f
©wuary©

A photomicrograph of a fertile egg that has been incubated for
two days. Cell differentiation and specialization have taken
place to the extent that the brain, heart, and blood vessels can
be recognized.

and albumen serve as food for the developing embryo and at
the same time keep it moist. The shell permits air to enter,
but prevents the ^*~~~' VolW

evaporation of ^.^mfiCW^^f.

moisture. Then
the mother bird
lays the egg, and
the development
of the embryo con-
tinues in the egg,
but external to the
mother's body.

In mammals, for
example the rabbit,
the entire develop-
ment is internal.
When the embryo
is completely developed into a young animal, very much like the
adult, it is born. The word " birth " is used to describe the process

of the little individual coming
forth after complete internal de-
velopment. This is in contrast
with hatching, which is the com-
ing forth of an animal from an
egg. During its internal devel-
opment, the mammalian embryo
is kept moist and warm within
the body of the mother. It is
fed by absorbing food from blood
vessels which pass through the
placenta of the mother organism.
There is a similarity in function between the placenta of flow-
ering plants and the placenta of mammals. They both are the

The unborn mammal is suspended in the
uterus by the umbilical cord. Surrounding
fluids serve as protection against shock. Food
for development is absorbed by osmosis
through the placenta.

290

REPRODUCTION OF ANIMALS

2 days

5 days

10 days

15 days

20 days

As development of the egg takes place, more and
more differentiation occurs. The yolk serves as the
food for the developing organism. First the cir-
culating system may be recognized, later the head,
limbs, and other organs. When the animal is com-
pletely developed, it pecks its way out of its shell.

QUESTIONS AND SUGGESTIONS 291

parts of the mother organism, through which the developing em-
bryos are fed. In the case of many plants, ducts and sieve tubes
pass through the placenta and through the seed stalk and thus
carry nourishment to the seed. In the case of mammals, the
blood vessels of the embryo extend into the placenta through
a cordlike structure somewhat similar to the seed stalk.

Questions and Suggestions

1. Name three differences between seeds and eggs.

2. Describe the spawning of frogs.

3. Give the following facts concerning the reproduction of the frog :
reproductive organs, the names of reproductive gametes, where ferti-
lization takes place (use the word external or internal), where the
organism develops, and the food of the developing embryo.

4. Discuss the complete development of the frog embryo.

5. Name the germ layers of the embryo and state the organs devel-
oping from each layer.

6. Using the outline headings given in question 3, fill in the out-
line for a flower, bird, and mammal.

Supplementary Readings

Atwood, Wm. H., and Heiss, Elwood D., Educational Biology (P. Blakiston's

Son & Co.).
Haupt, Arthur W., Fundamentals of Biology (McGraw-Hill Book Co.).
Holmes, S. J., General Biology (Harcourt, Brace & Co.).
Jewett, F. G., The Next Generation (Ginn and Co.).
Scott, George G., The Science of Biology (T. Y. Crowell Co.).
Wiggam, A. E., Fruit of the Family Tree (Bobbs-Merrill Co.).

CHAPTER XXXI

PROTECTION
OF YOUNG

The cat takes care of its
kitten.

The young kangaroo in its
mother's pouch.

What proportion of offspring lives to maturity? What is the relation
of the period of adolescence to length of life? Do all animals take
care of their young f What animals show the greatest parental in-
stinct f

We have already learned that all plants and animals start life as
single cells. In some species this single cell is a spore, in others
a zygospore, and in still others a fertile egg. Whether the crea-
ture is a Paramecium or an elephant, it started life as a single cell.

The offspring of simple organisms. When an amoeba, a bac-
terium, or any other one-celled organism divides into two new
cells, the production of the new individuals marks the disap-
pearance of the parent. It is impossible for the daughter cell and
the mother cell to exist at the same time. Yet, it would not be true
to say that the mother cell dies, for the protoplasm of which it
consisted continues to live in the two new daughter cells. Each
of the young amoebas is quite as capable of taking care of itself
as is the older individual from which each came. Except for the
growth in the comparatively short time between one cell division
and the next, which in the case of some organisms would be only
about twenty minutes, the young individual is in every way like
the full-grown individual. There is, probably, some difference in
size, however.

292

INFANCY AMONG SEED PLANTS 293

Among the lowest plants and animals that produce spores or
encysted cells, the new individual usually has a cell wall or coat
that is somewhat thickened. This is a means of protection against
drought, mechanical injury, or perhaps against the digestive juices
of some animal that might ingest it. The cell also contains a tiny
drop of oil or some other excess of food material that will sustain life
until the protoplasm is able to obtain food through its own activi-
ties. Such cells are usually produced in large numbers and are de-
posited in every current of water and air. Only a very small propor-
tion of such reproductive cells ever starts a new life. It is very largely
a matter of chance which one will and which one will not mature.
For example, mold spores are scattered by the bursting of the spo-
rangium. They are found practically everywhere ; but only those
that fall upon food in a favorable environment will develop.

Infancy among seed plants. In the seed-bearing plants, each
generation receives from the preceding one a great deal more
than a quantity of protoplasm. The gametes are produced in
proportionately small numbers, compared to the reproductive
elements of seedless plants. The female gametes especially are
very few, only one to each ovule. Then there is a great variety
of structures whose function is to make fertilization possible and
probable. For example, the display of the flower by means of
the showy corolla and fragrance will attract the insects that are
in search of nectar. In taking the nectar, the insects will be-
come covered with pollen which they will later, accidentally,
transfer to other flowers. The position and character of the
stigma of each flower show special adaptations to catch pollen,
and to aid and effect the formation of the pollen tube. All these
are parts of the equipment of the parent plants, which aid in the
process of fertilization.

The fertilized ovum or zygote is retained within the ovule. It
is supplied with nourishment which the young embryo uses up
in developing. The growth of the embryo goes on to a certain

294

PROTECTION OF YOUNG

Spanish nettle

acorn. blacictoerry-

— ,._- stem

See&

..style
r~6c:

. ., danSLelioa larkspur- * ^.w^t^
clematis 4 ocf>ple

men

Fruits and seeds are frequently adapted for dispersal from the parent plant. Winglike and
feathery structures are adaptations for wind dispersal ; barbs and sweet fleshy parts are adapta-
tions for dispersal by animals.

point and then stops. A surplus of nourishment, in the form
of endosperm or cotyledons, may be stored about the young em-
bryo. Additional protective covers generally grow about the seed.
All of these processes and structures are clearly related to pro-
tecting the young plant and supplying it with nourishment that
it can use until it develops the leaves which make its own food.
The seed cover, or the fruit, often possesses a variety of struc-
tures such as wings, stickers, fleshy pulp, or down, which aid the
young seed to travel some distance from the parent plant. These
structures are also the result of parental activity, and they con-
tribute to conditions that make for the favorable growth of the
young plant. If the young plants were to grow too close to the
parent plant, they might not secure sufficient sunlight for starch
manufacture nor enough minerals from the soil for protein man-

INFANCY AMONG LOWER ANIMALS

295

ufacture. The seed is protected while. within the fruit. It has
been supplied with food which it can use long after it has left the
ovary, and it has been supplied by the parent plant with some
adaptation in order to get away to a more favorable environment.
Infancy among lower animals. Frogs, fish, and other water
animals usually produce large numbers of eggs and sperms and
discharge these into the surrounding water. Probably many thou-
sand more sperms than eggs are produced. Even though a large
proportion of the eggs may become fertilized, most of the sperms
die as they greatly outnumber the eggs. Probably only a small
proportion of the fertilized eggs ever get far beyond the earliest
stages of development They are frequently devoured by animals
in the water. Because fertilization takes place in the water and
the embryos develop externally, a great majority of the young
die or are destroyed.

H. Armstrong Roberts
The mother hen watches over, shelters, and helps the chicks gather food.

296

PROTECTION OF YOUNG

There is very little care of the young among the lower animals
such as frogs and fishes. In many cases the parent dies before

the egg has had time to hatch.
The fertilized eggs are usually
left unprotected. In an occasional
species there is some evidence of
what may be called parental care.
For example, in some fishes, the
parent may find a protected spot,
as under a rock, and lay a mass
of eggs. The salmon and other
fish that spend part of their lives,
in salt water and part in fresh
water, migrate many miles up large
rivers and deposit eggs in shallow
water far from their natural en-
emies. Yet, of the one or two
million eggs laid by each female,
only a very few will ever reach
maturity. Among the crustaceans
(lobsters, crabs, shrimps) the female sometimes produces a sticky
fluid about the eggs. As the eggs come out of the body and be-
come fertilized, they are at- _ ., - . - - -
tached to the swimmerets on
the abdomen of the female
and remain there until the
embryos are ready to hatch.
Among the mollusks (oysters
and clams) the fertilized eggs
remain within the cavity of
the mother's mantle and so

are protected by the shell until the young hatch and are able to
swim.

Museum of Natural History

The female lobster carries the eggs while
they are developing. Special hairs attached
to the appendages of the abdomen secrete
a sticky substance which holds the eggs in
place. This secures protection.

The female crayfish not only carries her eggs
attached to the swimmerets, but by straightening
her abdomen and waving the swimmerets brings
the eggs in contact with a supply of oxygen.

INFANCY AMONG INSECTS

297

Infancy among insects. There is a wide range of egg-laying
habits among insects. Some kinds of insects leave the eggs almost
anywhere. Others lay the
eggs in a material that is
likely to furnish food for
the young as soon as the
eggs hatch. The grasshop-
per lays her eggs in the
ground and never sees them
again. The butterfly lays
her eggs on a leaf and,
shortly afterwards, dies.
The fly deposits eggs in de-
caying meat or other or-
ganic matter so that food

. 1/11 The butterfly usually lays her eggs on the food that

IS present IOr the fly larvae wUl be used by the tiny larvae. When the little cater-

i . i -. j £ j pillars emerge from the eggs, they begin to eat the

Wnicn natcn OUt 01 the eggS. leaves upon which they hatched.

The elaborate preparation for the laying of eggs of ants, bees,

wasps, and termites is remark-
able. The solitary wasps show
great industry and ingenuity in
building their nests, in catching
caterpillars or spiders, in treating
■-x&*J$j&S£^*c the prey to prevent decay, and

in packing these victims into a
nest with the eggs. The adults
die or fly away shortly after

In the autumn, the female grasshopper lays completing Such a nest, and they
fertilized eggs in a hole she digs in the ground. .

These eggs stay in the ground during the winter, never have a chance to See their
The rays from the sun of the late spring warm _ . , .

the earth and incubate the eggs. Small newly Onspnng. In the bee COlony,

hatched grasshoppers crawl from the earth. , , i i l

the young are remarkably pro-
tected. The eggs are laid in certain cells of the hive. When the
egg hatches into a minute, footless grub or larva, it is fed for the

WH. FITZ. AD. BIO. — 20

298

PROTECTION OF YOUNG

first few days on rich food produced in the stomach of certain of
the worker bees that act as nurses. Later, they are fed with a

The digger wasp fills her nest with spiders stung in such a way as to paralyze and preserve
them. An egg is laid on each spider; when the larva hatches it is well supplied with food.

mixture of pollen and honey. Certain of the worker bees act as
soldiers to guard the hive.

Infancy among birds. Among the birds, the new individual
receives a large amount of protection and food for a very long
period. After fertilization, which takes place inside the mother,
the egg immediately starts to develop. The yolk and albumen
represent large food supplies, and the shell is an effective protec-
tion. After the egg is laid in a specially made nest, the develop-
ing embryo is kept warm by the parent's body. This is known
as incubation. It makes possible a safe and rapid development.

Both the parents of many species of birds take part in the
nest-building, in protecting the nest, and in incubating the eggs.
When the young of some species come out of the eggs, they are
fully developed and very much like the adult. The young chick,
for example, begins to walk and to pick up food particles almost

INFANCY AMONG MAMMALS

299

immediately. Among other birds, such as robins and eagles, the
young birds are quite helpless. ■ The feathers have not developed,
the eyes are closed, and the nestlings are not able to feed them-
selves. The parents fly about gathering insects, fish, lambs, or
whatever it is that constitutes their food. They bring this food
home to the nestlings. They protect them from other animals
and teach them, in due time, how to fly and get food for them-
selves. Only when the young are strong enough to fly and forage
for themselves are they put out of the nest. Birds lay compara-
tively few eggs because, due to internal fertilization and parental
care, each egg produced is almost sure to develop into a young
animal. Birds usually lay one egg at a time, and when the number
that is usual for the particular variety
of bird is reached, the parents start
to incubate the eggs. Compare this
number, one to sixteen, with the mil-
lions of eggs produced by the salmon
and the lack of parental care after
the salmon eggs are laid and sprayed
with milt.

Infancy among mammals. The
embryo of a mammal is protected, by
the mother's body, a longer time than
that of any other animal. During
this period, development goes on,
and at birth, the young is easily rec-
ognizable as belonging to a particular
species. The embryos of different
species take varying lengths of time
to develop. The rabbit develops
from the fertile egg in three weeks and

then is born ; the human baby needs about nine months ; and the
elephant about two years. This shows remarkably rapid develop-

Care of young is often shown by
birds. The tailor bird weaves an elab-
orate hanging nest in which the eggs
are hatched and the young cared for.
Both the mother and father birds brood
over them. One forages for food while
the other keeps the nestlings warm.

300

PROTECTION OF YOUNG

N. Y. Zoological Soc.

ment of cells considering the fact that
each" animal originated as a single
fertilized cell.
The kangaroo and the other mar-
supials, pouch animals, give birth to the young while these are
still poorly developed. The babies crawl into the pouch on the
mother's abdomen. The skin lining this pouch contains glands
that secrete a milky fluid by means of which the young kanga-
roos feed. All female mammals have well-developed milk glands
and normally suckle their young for a long or short period of time.
Some mammals are able to stand or walk immediately after
birth. This is true of the calf and of grazing animals generally.
Among other species, the new-born young is completely helpless.
The kitten does not open its eyes for several days. The human

N. Y. Zoological Soc.

Care of young reaches its heights among the mammals.

INFANCY IN MAN

301

N. Y. Zoological Soc.

baby does not begin to walk for a
year or more. Generally, we „find
that the higher the species the longer
the infant depends on its parents for
protection and nourishment.

Infancy in man. In man, protection of the young is shown in
the highest degree. Not only is there a long period of dependence
of the baby upon the nourishment obtained from the mother's
body before birth, but there is a long period of suckling after birth.
The greatest care and protection are given the young during its
infancy and childhood. As communities become more prosperous,
there is a tendency on the part of the parent to postpone for each
child the assumption of individual responsibilities.

Among the different races of mankind, and even among different
peoples of the same race, there is a great deal of variation with

N. Y. Zoological Soc
Note the length of infancy given in the table on the following page.

302

PROTECTION OF YOUNG
TABLE OF ADOLESCENCE

Animal

Growing Period

Length of Life

Elephant (Asiatic or
Indian) ....

Full grown but not fully
mature at 25 years.
Full vigor and strength

. at 35.

70 to 80 years.

Camel - .

4 to 6 years.

20, very rarely 35 to 40.

Horse . . .

3 to 4 years.

18 to 30 years ; very
rarely to 40 years.

Cattle . . .

3 to 4 years.

14 to 20 years.

Sheep . . .

1 to 2 years.

6 to 10 years.

Pig ... .

1 to 2 years.

6 to 12 years.

Dog. . . .

• 2 years.

12 years.

Norway Rat
norvegicus)

(Mus

14 months.

3 years.

Cat . . . .

1 to 2 years.

12 years.

Lion .

3 to 4 years.

12 to 20 years.

Man . . .

20 to 25 years.

65 to 75 years.

Compiled by Dr. C. V. Noback, New York Zoological Park.

regard to the prolongation of infancy. In general, development is
found to be more rapid in warm countries than it is in colder
regions. For this reason maturity, in practically all forms, is
reached at an earlier age among peoples in the tropics and semi-
tropics than among those who live in temperate and colder coun-
tries. This, however, cannot be accepted without admitting an

DEVELOPMENT OF PARENTHOOD 303

exception. The Eskimos, for example, mature, in general, at an
earlier age than the English. There are, no doubt, other factors

m W \

v W *?- Jfl 1

1 Fk r^k

J^^^^M

(Madame Le Brun and her daughter.)

All through the ages, artists, in their works of art, have expressed mother
love and the dependence of children.

than climate that influence development and maturity. It is
probable that nutrition has an influence. There is also another
side to be considered, for rapid development or early maturing is,
generally, connected with relatively shortened duration of life.
The average length of life and the proportional number of people
of advanced age are usually greater in those communities that
give the children a longer period in which to develop, protect them
more completely from various dangers, and look after their needs
more thoroughly.

Development of parenthood. Among the simplest organisms,
there is no period of life corresponding to parenthood. At a certain

304 PROTECTION OF YOUNG

phase in the organism's growth, it divides into two parts, In the
act of reproduction, it ends its own existence. Among the higher
organisms, especially birds and mammals, reproduction of new
individuals is generally repeated for a long or short period of
years. A considerable portion of the individual's activities has
to do with preparing for and caring for the young. In man-
kind, parenthood often makes a greater demand upon the individ-
ual than just making a living. On the other hand, the increased
activities of adults for the young make possible for each genera-
tion a better preparation and a richer equipment for life. So
much that concerns and so much that is of value to humans lie
beyond the problems of making a living in the material sense.

Questions and Suggestions

1. What are the advantages to a species in producing eggs or
seeds ? What disadvantages ?

2. Explain the necessity for such a tremendously large egg produc-
tion among fish as compared with the small production among birds.

3. How can an organism make provision for offspring that it can
never see or know ?

4. What are some of the advantages of prolonged infancy ? What
are some disadvantages ?

5. How may animals that look after their young benefit from such
activities ?

6. How can plants be said to take care of their young ?

7. What are some of the dangers from which the young of plants
must be protected ?

8. What are some of the dangers from which the young of animals
must be protected ?

9. Discuss whether or not a kitten's development can be hurried
by forcing its eyes open ?

10. Discuss whether there is any way of hastening or slowing up the
development of a plant or an animal ?

11. Make a special report on the breeding habits of the stickle-
back or some other nest-building fish.

12. Give a report on the migrations and breeding habits of the
salmon or of the eel.

13. Give a report on the breeding habits of the " obstetrical toad "
and compare these with the breeding habits of common toads.

SUPPLEMENTARY READINGS 305

14. Report on the migrations and nest-building of the egret, cow-
bird, or some particular species of bird to show the relation of these
activities to the protection and welfare of the young.

15. Give a library report on the care of their young by ants.

16. Give a library report on the care of their young by spiders.

17. Describe the domestic life of some carnivorous mammals.

18. Report on the community life of the beaver with special regard
to the care of the young.

19. Report on the social life of some anthropoid.

Supplementary Readings

Guyer, Michael F., Being Well Born; An Introduction to Heredity and Eugenics

(Bobbs-Merrill Co.).
Haupt, A. W., Fundamentals of Biology (McGraw-Hill Book Co.).
Holmes, S. J., General Biology (Harcourt, Brace and Co.).
Jewett, Mrs. F., The Next Generation (Ginn and Co.).

CHAPTER XXXII

CHARACTER
OF OFFSPRING

EpA

^jpF//j

f ii

m "1

Br- **

■ 1

1L ^.

Museum of Natural History
Turtle Eggs.

Museum of Natural History
Dinosaur Eggs.

What characters can be inherited f What is the relation of environ-
ment to heredity •? Can a person consciously influence his inherit-
ance? What constitutes good environment?

Variety in protoplasm. The fact that the living matter of all
plants and animals is protoplasm, has already been discussed. All
protoplasm is alike in certain of the elements that compose it ; it
is alike in its growth by assimilation, its sensitiveness to stimula-
tions, and its response to these stimulations. Yet protoplasm of
one species is different from that of another. The protoplasm
of a squash seed, for example, develops only into a squash vine
and never into a rosebush, never into a canary. The protoplasm
of a wren's egg develops into a wren, never into a willow tree nor
a wolf. These differences are thought to be located in certain
parts of the chromosomes called genes. These genes are the real
carriers of hereditary traits. By a gene is meant the part or unit
factor of the chromosome, which is supposed to represent an
hereditary character. The development of the organism depends
largely upon the character-determiners of the genes.

A many-celled organism grows by the individual cells dividing
mitotically. In this mitotic division, each chromosome splits into
two parts exactly alike. Hence, the chromosomes in all cells

306

VARIETY IN PROTOPLASM

307

derived from one cell will be alike. The squash seed contains
protoplasm that is a combination of the protoplasm of the parent
plants. The protoplasm in the fertile egg of a frog is a part
and a continuation of the protoplasm of the parents of the frog.
Each kind of protoplasm continues to be much the same, genera-
tion after generation.

There is no difficulty in recognizing maple trees, because all
maple trees resemble each other. Bean plants resemble bean
plants. Elephants resemble elephants. All the individuals of a
species are much alike. Yet no two individuals are ever exactly
alike. We might call by name and know several hundreds of the

♦EXAMPLES OF CHROMOSOME NUMBERS
(in Animals and Plants)

Common Name

Scientific Name

Group

In Body
Cells

In Gam-
etes

Sponge

Sycandra raphanus

Porifera

Hydra

Hydra fusca

Coelenterata

Earthworm

Lumbricus herculeus

Annelida

Snail, fresh water

Paludina vivipara

Mollusca

Crayfish

Cambarus virilis

Crustacea

200

100

Malarial mosquito

Anopheles punctipennis

Insecta

House mosquito

Culex pipiens

Insecta

House fly

Musca domestica

Insecta

Starfish

Asterias vulgaris

Echinodermata

Frog

Rana catesbiana

Vertebrata

Chicken

Gallus domesticus

Vertebrata

Cat

Felis catus

Vertebrata

35 and 36

17 and 18

Dog

Canis familiaris

Vertebrata

21 and 22

10 and 11

Horse

Equus caballus

Vertebrata

Monkey

Macacus rhesus

Vertebrata

Man

Homo sapiens

Vertebrata

Spirogyra

Spirogyra neglecta

Thallophyta

Moss

Sphagnum squarrosium

Bryophyta

Bracken fern

Pteris aquilina

Pteridophyta

Pine

Pinus sylvestris

Gymnospermae

Pea

Pisum sativum

Angiospermae

Wheat

Triticum vulgare

Angiospermae

Corn

Zea mays

Angiospermae

♦Reprinted by permission from Wilson: The Cell in Development and Heredity (1925) by
The Macmillan Co.

308

CHARACTER OF OFFSPRING

pupils of our school. Scientists distinguish, in a like manner, thou-
sands of individuals of one species of a plant or animal. These

International News Service
Variations in the heads of birds. All the birds in
the picture may be descendants of the same original
ancestor. Compare these with others that you know.

are all enough alike to be classed as insects, pigeons, or dahlia
plants ; but each is different in some way from all the others.

The problems of these likenesses and differences are the problems
of heredity. The study of heredity includes a study of all the
various characteristics in the offspring that are more or less similar
to those characters of the ancestors.

Environment influencing development. Individuals of the
same species may differ because all do not have exactly the same
conditions during their early development. Differences in tem-
perature, in the relative amount of moisture, in the character of
weather, or of food may cause plants to be stunted or slow to
flower in one region when compared with the similar plants of
another region. A more abundant supply of mineral salts, or more
sunshine at certain periods, may produce plants that are some-
what better developed than others grown from the seeds of the
same parent plant. Every farm, every roadside, and every city lot
furnish examples of plants that have thrived better or worse than
their neighbors, because of variations in their environments.

Temperature, moisture, light, and food are some of the factors
that influence the development of animals as well as of plants.
The male of the European bullfinch has a bright red breast ; the
female is entirely brown. If the male bird is fed on hempseed, its
plumage changes to a dull color similar to the female. Among honey-

ENVIRONMENT INFLUENCING DEVELOPMENT 309

bees, a given egg may develop either into a worker or into a queen.
This development depends upon the nourishment that the larva
receives. It is thought by some investigators that the kind of food
(honey or pollen) may cause the differentiation in the growing larva.
Others think that when a larva is given large amounts of foods, it
becomes a queen ; if a small amount of food, it becomes a worker.

Many abnormal forms result from a variety of unfavorable con-
ditions during development. This is true in human beings as well
as in other species. Even where the results are not abnormal,
inequalities of environment bring about differences among individ-
uals of the same species. For example, lack of Vitamin D in the
diet results in bone deformities. Lack of iodine may give rise
to cretins. Too much food is likely to make people fat.

Trees may become distorted by the wind. Plants grown in
poorly-lighted places show an irregular development as the result
of a one-sided illumination. Well-fed cows give more milk than
poorly-fed cows. The lizards and spiders of Mammoth Cave,
Kentucky, are colorless. Exposure to sunlight is thought to
increase the amount of pigment in the human skin. One who has
learned to swim behaves differently in the water from one who
has not learned to swim. A trained horse runs faster than an
untrained horse of the same parentage. A child who has re-
covered from measles does not get the disease a second time
when exposed to the infection. One can become accustomed to
cold weather or to rainy climate. One can become skillful in
some art or game as a result of practice; or his muscles can
become weak after a period of disease or disuse.

Where the differences between two individuals result from
differences in outward conditions, or from environment, the prac-
tical problem is to find out how to treat plants or animals so as to
get the desired results. Will one kind of fertilizer or mineral salts
result in more cotton per acre ? Will one kind of food produce more
milk per cow? If so, an adjustment can be made so that the

310

CHARACTER OF OFFSPRING

Japanese spaniel

Pug

French poodle

Beagle

organism in question will benefit. Will one
system of training make all individuals musi-
cal, or quick at figures, or skillful in ath-
letics ? If so, and if it is desirable, the system
should be investigated and applied to all
children.

All of these examples, and others which
they may suggest, are proof that plants and
animals are influenced by what happens to
them. These differences that depend upon
the environment are known as variations.
Because they affect the body cells of the
organisms and not the germ cells they are
also called somatic (body) variations. They
affect the individual without affecting, to any
extent, the offspring of that individual.

Ancestry influences development. The
careful farmer or animal raiser has learned
to select the seeds for his planting, or the
animals which he is to use for breeding.
Large seeds are more valuable than small
seeds, especially when a seed crop, such as
beans or peas, is desired. A healthy cow
that gives a relatively large amount of milk
is a more promising mother for good calves
than a cow that yields only a small quantity

Collie

Airedale

English setter
All dogs probably originated

ANCESTRY INFLUENCES DEVELOPMENT

311

of milk. The ability to produce a large
quantity of milk is a trait transmitted
from parent to offspring. If the farmer
is interested in eggs for market, he
selects hens that lay over 200 eggs a
year, and uses these eggs for hatching
purposes. These offspring, with a few
exceptions, are good egg-layers. This
trait, too, seems to be an hereditary one.
For centuries, those engaged in plant
and animal industries have selected the
best individuals and the best seeds for
continuing or improving their stock.

Certain differences are found among
cotton plants and corn plants, among
cows and horses, among human beings,
and, in fact, among all organisms that
seem to have nothing to do with the
kind of treatment they get. Some cot-
ton plants produce long fibers and
others short fibers, because they come
from certain stock. They belong to a
particular breed. Some calves become •
Holstein cows and others become Jersey
cows, no matter how they are fed.

English bulldog

Scotch terrier

Greyhound

Dachshund

St. Bernard
from the same ancestor.

Mastiff

American fox hound

312

CHARACTER OF OFFSPRING

0.0-rYELLOW
1.5;; WHITE

7.5—RUBY

20.0—CUT

0.0 T STAR

9.0— TRUNCATE

14.0

27.5-fTAN

29.0-

33.0-J- V ^oN IL " 33.0-j-S
36.1"MIN1ATURE

13.0- -SABLE

GARNET 46.5- "BLACK

S6.5,; ^FORKED

65.0- -CLEFT
68.0--BOBBED

97.5
98.5

103.0
105.0

R0UGH-0.Q4^BENT
OID 0.51SHAVEN
0.9 EYELESS

STREAK

25.3 ,5EPIA
25.8-- HAIRY

38.5f-DlCHAETE
42.0 :L SCARLET
45.5HI-PINK

SPINELESS
B1TH0RAX
59.0+ GLASS

63.5- -DELTA

65. S
67.5

HAIRLESS
EBONY

In the same incubator, under like conditions of moisture and
temperature, some eggs hatch into Rhode Island Reds and some

into Plymouth Rocks.
One horse is said to in-
herit a definite coat color,
a certain shape, or the
ability to run rapidly or
to pull heavy loads.
These characters are part
of his breed. The John-
son children are known
to be tall and the Brown
children are short, al-
though they all seem to
be given good food and
care. They inherit their
stature. In addition to
anything in the environ-
ment, which may influ-
ence the qualities or
characteristics of indi-
viduals, there is some-
thing with which the
individual is born. Some-
thing that influences his
development and makes
him different from others
that live in the same environment. The characters that are
inherent in the individual are known as germinal variations. They
are a part of the ancestry because they are in the genes of the
chromosomes in the fertilized cell. They can be transmitted from
parent to offspring because they are a part of the germ plasm in the
egg and sperm.

70.0: r LOBE
73.5" -CURVED

88.0- -HUMPY

ARC

95.4

U/-- 95.7'

PLEXUS

101. 0-t M1NUTE-G
BROWN
SPECK

72.0- -WHITE-OCELLI

86 .5- ROUGH

,CLARET
MINUTE

After Morgan
Through careful experimentation, definite parts of
chromosomes in the fruit fly have been found to be re-
lated to definite structures. Scientists have mapped on
the chromosomes of the fruit fly, the location of the genes
which carry certain definite characters.

EFFECT OF ENVIRONMENT ON INHERITANCE 313

How the genes behave is a problem of heredity. Experience
has shown, that as a result of selection it is possible not only to
maintain the quality of the stock, but also to improve it, up to a
certain point. Wherever selection is neglected, the cultivated
plants or domestic animals deteriorate in quality. They deteri-
orate whenever the food or any living condition is neglected.
The rule of the successful breeder is to select animals or plants
showing the best ancestry. Then he should provide the best con-
ditions for their healthy growth and development.

Effect of environment on ancestral traits.' An unborn child may
be influenced by conditions prevailing in either parent. Malnu-
trition or serious ill-health on the part of the mother has an injurious
effect on the offspring. Severe shock or grief, worry, nervous
exhaustion, the influence of a very few diseases, lead, mercury, or
alcohol poisons in the blood or tissues may act detrimentally on
the unborn offspring. The effect of these conditions or materials
is to interrupt the proper nutrition of the offspring, directly poison
it, or, by generating toxins in the mother, poison the developing
embryo. Disease-toxins affect unborn children to such an extent
as to sometimes cause malformations, arrested development,
instabilities of the nervous system, general physical or mental
weaknesses, or even death before birth. The children of inebriates
comprise a striking proportion of criminals, imbeciles, and those
with predispositions toward certain diseases. All of these effects
are environmental effects, not inherited effects. The character of
the environment of the child before and after birth is a factor
of great importance in the development of the child.

Many prospective mothers think they can develop musical
ability in a child by studying and playing music before the child
is born. Or they hope they may produce beauty in the child by
long contemplation of a picture of a beautiful child. The expla-
nation frequently given for birthmarks is that the mother ate
many strawberries or tomatoes before the child was born or she was

WH. FITZ. AD. BIO. — 21

314

CHARACTER OF OFFSPRING

Very similar twin girls.

1 •» 1

9 4 i»

/rcf ra^ Chidnoff
A recent photograph of the same identical twins. It is
very difficult to distinguish one from the other.

frightened by a fire. If the
birthmark has hair growing on
it, the explanation given is that
a mouse frightened the mother
before the child was born.
Structural changes cannot be
produced in a child by mater-
nal impressions or mental ex-
periences of the mother/ The
physiological explanation of
birthmarks is that a number of
small blood vessels of the
skin of a new-born infant
have remained dilated in a
particular spot. This is a'
somatic, not a germinal
variation.

The characters com-
bined in the chromosomes
during the union of the
sperm and egg are the
characters that will de-
velop in the child. If
musical ability is in one of
the genes, it will be pres-
ent in that of the off-
spring. If not, no amount
of practice on the part of
the parent will develop the
talent. The only struc-
tural changes made in the
offspring are those that
can be affected by good

DIFFERENCES AMONG OFFSPRING

315

or poor nutrition Or toxic materials of one sort or another. Only
by affecting germ cells can the character of the offspring be con-
trolled or changed. Recently, it has been demonstrated that in-
ternal secretions circulating in the blood of the parent may affect
the germ cells. Thus, if a mother's thyroid is overactive and too
much thyroxin circulates in the blood, the germ cell may be
affected in such a way that abnormalities in the developing off-
spring are frequently brought about.

Differences among offspring. It has long been known that
certain characteristics or qualities reappear in successive genera-
tions. Why do not all the characteristics of the parents reappear ?
If each new individual were merely a portion of an older individual,
it could readily be seen how the characters would continue from one
generation to the next. When plants are propagated by cuttings
or by grafts, the plants thus produced remain rather uniform.
Where reproduction is sexual, two germ cells, the gametes, come
from different sources. Each germ cell carries many qual-
ities that are characteristic of the protoplasm of each parent.
These qualities reappear with a certain degree of probability and in
relationship after the two germ cells have united. Each individual
resembles both parents, but, necessarily, also differs from both

When two coins are tossed a great number of times, two tails turn up 25% of the times, two heads
turn up 25% of the times and one head and one tail turn up 50% of the time. This occurrence
is called the law of chance. In the few matchings shown in the diagram, the result would prob-
ably not be as near the 25, 50, 25 ratio as is pictured. This illustrates the law of chance (page 317).

parents. A child may have brown eyes like the mother's and curly
hair like the father's. Offspring of the same parents also differ

310

CHARACTER OF OFFSPRING

mL|

When peas are rolled down an inclined plane through a
small opening against nails, they line up in pens in a very
definite order. When this experiment is performed, a
sorting out, known as a normal distribution, occurs. Few
peas are found in the end pens, many in the center. This
illustrates the law of chance, discussed on p. 317.

from each other. Some are tall and some are short, some are
blue-eyed and some are brown-eyed. This will be explained later.

We have learned that
a process called matura-
tion or ripening occurs
in the development of
mature germ cells in the
parent organism. This
maturation of the germ
cells accounts for the
differences among off-
spring. Chromosomes
are thought to possess
combinations of char-
acter-determiners called
genes. These genes are
found to be in pairs in the primary sex cells. During the matu-
ration process, reduction takes place. In reduction, one member
of each pair goes to a given germ cell. Consequently, each germ
cell has one half the number of chromosomes found in the pri-
mary sex cell. If the primary sex cell had a pair of character-
determiners for eye color, one of this pair carries blue and the
other brown, the chromosome containing the gene for blue eyes
would go to one germ cell and the chromosome containing the
gene for brown eyes would go to another germ cell. A primary
sex cell may have two characters Tor a particular trait, but a germ
cell only has one and is pure in regard to any particular trait.
Consequently, the same organism may produce germ cells with
unlike characters. The sperm cells of the male are not identical ;
eggs, too, have different character-determiners or genes in them.
When the sperm and egg meet in the process of fertilization, the
characters of the fertilized egg depend upon the characters in the
genes in the combined chromosomes of both the sperm and egg.

QUESTIONS AND SUGGESTIONS 317

These combine according to the law of chance. Combinations of
a pair of characters follow a definite proportion.

Problem. How may the law of chance be demonstrated f

I. Put in a jar one hundred black beans and one hundred white beans of
the same size. Mix the beans thoroughly. Without looking, take out two
beans at a time.

A. Score the number of times two black beans, two white beans, and
one black and one white bean are taken out.

B. At least one hundred pairs should be taken out before the scores
are summarized.

C. State the proportion of two black to a combination of one white
and one black, and to two white.

II. Toss two coins at least one hundred times before totaling your scores.

A. Score the number of times two tails appear.

B. Score the number of times two heads appear. •

C. Score the number of times one tail and one head appear.

D. State the proportion of two heads to a combination of one head
and one tail, and to two tails.

III. When it is purely chance that controls the meeting of members of a
pair of characters, the proportion resembles that obtained with the beans and
coins. In order to get a proportion, the experiment should be carried on a large
number of times.

Questions and Suggestions

1. In what structures of germ cells are characters of organisms
located ?

2. What is meant by heredity ?

3. What effect has environment on development ? Give examples.

4. What effect has ancestry on development ? Give examples.

5. What effect has environment on ancestral traits ?

6. Account for differences among offspring.

7. How can the best offspring be obtained ?

8. Discuss the law of chance. Describe an experiment to illustrate
it.

9. How does the law of chance operate in the fertilization of an
egg by sperm ?

CHAPTER XXXIII
HEREDITY

Gregor Mendel

Thomas Hunt Morgan

What are Mendel's laws of inheritance f How were they formulated f
Do these laws of inheritance hold true for all plants and animals f

It has been found that truly heritable traits or characteristics
of an individual are comparatively independent of each other and
may be inherited independently. These characters are called
unit characters. If the members of a pair of unit characters meet
in an offspring, each member retains its identity and each char-
acter of the pair may be separated in subsequent generations. The
following illustration is an example of the behavior of a pair of unit
characters.

Incomplete dominance. There are two distinct kinds of Anda-
lusian fowls, one having white feathers splashed with black ; and
the other, black feathers. The black fowls are known as pure black
because, for generations, their ancestors have been black, have
mated, and have given rise to only black descendants. The
splashed-white fowls are known as pure white; their ancestors
were white, they bred with white, and have always produced white
offspring. A fowl from each group was selected as a parent.
They were mated, fertile eggs were laid and incubated, and the
outcome of the experiment awaited. Would the chickens be black,
or white, or a mixture of the two colors ? Although the experi-
ment was repeated several times, the results were always the same.

318

INCOMPLETE DOMINANCE 319

All the young chicks were a queer mixture of mottled black and
white which is known as blue. They were mixtures and not pure
bred like their parents. When the members of a pair of widely
different unit characters, in this example, black and white feathers,
meet in an offspring, the offspring is called a hybrid. Evidently,
neither the black nor the white character could mask or dominate
the other, and a blending took place. The blending of a pair of
characters is called incomplete dominance.

Next, the investigators wished to discover what the descendants
of the hybrids would be like. Only blue Andalusian fowls, hybrids,
were chosen for this part of the experiment. This hybrid gener-
ation is known as the Fi generation or the first filial generation. It
was found that the offspring of hybrids varied in color. Some were
blue like their parents, some were white like one grandparent and
some were black like the other grandparent. When a large number
of them were examined, it was found that the different colors of
the chicks always occurred in the same proportion. For every two
chickens that were blue like their parents, there was one black
and one white chicken. In other words, 25 per cent were black,
25 per cent were white, and 50 per cent were blue. This genera-
tion, in which there was a reversal to ancestral type by the segre-
gation of the original unit characters, is known as the second filial
or the F 2 generation. Evidently, the original characters must have
retained their identity since some of the offspring showed one char-
acter and others showed the opposite character.

The next step in the experiment was to find what would happen
when the different members of this mixed group became parents.
A black fowl was mated with another black and all the offspring
were black. In other words, the black chickens of the F 2 gener-
ation not only looked black like their black grandparents, but were
pure as shown by the fact that they had only black descendants.
They possessed only genes or character-determiners for black.

A white of the F 2 generation was mated with another white and

320

HEREDITY

all their offspring were pure white. But when blue fowls were
mated with others like themselves, some of their offspring were

ft >W* *>$# *>£

If a black Andalusian cock is mated with a white Andalusian hen, the offspring is a hybrid
showing a mottled blending of the black and white called blue. This is an example of incom-
plete dominance. If a blue cock is mated with a blue hen, 25 per cent of the offspring will
probably be black, 50 per cent may be blue, and 25 per cent may be white. Black pairs will breed
only black; the white pairs will breed only white ; but the offspring of a blue pair will segre-
gate, sort out, into black, blue, and white.

black, some were white, and some blue. The blue chickens, then,
of the F 2 generation were hybrids.

The inheritance of color in the Andalusian fowl is :

(1) Pure black mated with pure black will always produce pure
black.

(2) Pure white mated with pure white will always produce pure
white.

(3) Pure black mated with pure white will always produce 100
per cent blue hybrids.

(4) Blue hybrids, when mated with blue hybrids, tend to pro-
duce 25 per cent black, 25 per cent white, and 50 per cent blue.

The four-o'clock is another example of an organism in which a
hybrid, produced by two distinct species, is unlike either, but is a
blend of the two. The pure lines or types of four-o'clocks have

EXPERIMENTS IN PLANT BREEDING

321

either red flowers or white flowers. If red flowers are pollinated
with pollen from red flowers, their seeds will produce red flowers.
If white flowers are pollinated with pollen from white flowers, their
seeds will produce plants with white flowers. But if red flowers
are pollinated with pollen from white flowers, or white flowers with
pollen from red flowers, the seeds will produce plants bearing pink
flowers. This pink is a blend of the white and red colors. A
flower of this type and the seed that produces it is called a hybrid.
If these hybrids are allowed to pollinate themselves, their seeds

^Parents

The hybrids of the Japanese four-o'clock show incomplete dominance. The pure generation
is usually called the parental, P ; the hybrid generation is the Fi ; and the next generation
showing segregation is the F 2 . The little circles represent gametes and are colored to show
genes or the color determiners which each flower carries.

322 HEREDITY

will produce plants which will bear flowers of three colors.
Of every 1000 blossoms, approximately 250 will be red, 250 will
be white, and 500 will be pink. The colors will be in the proportion
of 1 : 1 : 2. The various colors of the four-o'clocks of succeeding gen-
erations will vary in the same way as those of the Andalusian fowl.

Experiments in plant breeding. Long before the foregoing
experiments were carried on, Gregor Johann Mendel (1822-1884),
an Austrian priest and head of a monastery, was especially inter-
ested in cultivating garden peas. He found that his pea plants
differed from each other in very many characters. Tallness, col-
oration of seeds petals, and pods, and the hairiness, roughness,
or smoothness of skin on the seeds and stems were some of the
differences that he observed. Then he asked, " How does a partic-
ular quality carry over generation after generation ?-" He pro-
ceeded to seek the answer to his problem by experimentation.
He selected tall plants and kept them in a certain garden plot.
Away from these he raised a plot of plants that were always short.
He called each group a pure-type. The unit character of height
was one particular trait in which he was interested. He crossed
pairs of plants which differed in this single character. He repeated
his experiments to investigate other out-standing characters. Tall
plants were crossed with short; plants with yellow seed coats
with those of green seed coats ; plants having smooth seeds with
those having rough seeds; hairy stemmed plants with hairless
stemmed ones. In each of these crosses he watched the behavior
of the variations of a single character only. After many experi-
ments, Mendel learned and made known some very important
principles.

The Mendelian laws of inheritance. — The Law of Dominance.
When two of the pea plants that differed from each other in one
characteristic were crossed, all the offspring resembled one of the
two parents in regard to that characteristic. If one parent were tall
and the other short, all of the next generation would be tall.

THE MENDELIAN LAW OF DOMINANCE 323

Gregor Johann Mendel planted peas in his garden in Briinn, Austria. He crossed plants
showing different characters and produced a variety of hybrids.

If one of the parents were of a wrinkled-seed variety and one of a
smooth-seed variety, all of the next generation would have smooth
seeds. If one of the parents had a yellow seed coat and the other
had a green seed coat, all of their offspring had yellow seed coats.
To get more accurate results, he pollinated artificially the flowers
of two varieties and kept them protected from all insects. The
seeds from these plants were gathered, planted, and the new
plants were carefully watched. Mendel found that the characters
did not blend, as was later noted in the Andalusian fowl. One
character completely dominated the other character and concealed
it. This is called complete dominance. It has been found to occur
in many species of plants and animals, and is true for many dif-
ferent characters. This is known as Mendel's Law of Dominance.
Dominance, as used in studies of heredity, is a condition in which
one of a pair of characters will appear in the offspring and hide or
mask the other. The character that shows in the offspring is

324

HEREDITY

op-

°o°

T 2

GO
Q

called the dominant character. The second quality, the one that
does not show, although it is actually present, is known as

the recessive character.
Whatever there is in the
protoplasm that pro-
duces the recessive qual-
ity, it is not destroyed
in the crossing, for, as
shall be seen, the quality
may reappear in later
generations. In the ex-
ample given, the domi-
nant traits were tall
plants, smooth seed, and
yellow seed coats. The
recessive traits were
short plants, wrinkled
seeds, and green seed
coats. The individual
resulting from a cross of opposite characters is called a hybrid.
For example, when plants with yellow seed coats are crossed with
those with green seed coats, the offspring appear yellow. Because
one of the parents had green seed coats the protoplasm of the
offspring must be different. These yellow offspring are hybrids
since they conceal the character determined for green. In all
external appearances, hybrids resemble pure dominants.

Mendelian Law of Segregation. Although the tall descendants
of a mixed parentage, that is, a tall and a short, may appear tall
like one of the parents, its protoplasm or part of its protoplasm
is really different. This must be true since it has been built up
in part from the protoplasm of the short parent. In the same
way, the plant with the yellow seed coat of mixed parentage may
resemble, in seed coat color, one of the parents, but it is still a

When pollen from a pea plant that produces smooth seeds
is transferred to a plant that- produces wrinkled seeds the
resulting plants will produce smooth seeds. In peas,
smooth seed coat dominates a wrinkled seed coat. The
resulting offspring are hybrid, for when they are self-
pollinated their offspring show 75 per cent smooth seeds
and 25 per cent wrinkled seeds ; of the 75 per cent smooth
seeds, 25 per cent is pure bred smooth, and 50 per cent is
hybrid smooth. This illustrates complete dominance, be-
cause smooth seed coat completely dominates wrinkled
seed coat and does not blend with it.

MENDELIAN LAW OF SEGREGATION

325

descendant of the green seed coat stock, and its protoplasm is
probably different. Mendel made further experiments with his
peas to find out what happened in later generations. He made
three kinds of crosses: (1) he cross-pollinated a hybrid with the
dominant parental type ; (2) he crossed a hybrid with the recessive
parental type ; and (3) he crossed a hybrid with a hybrid.

Consider the third experiment first. When hybrids were self
pollinated, their seeds always produced species of both ancestral
types. For example, hybrid peas with yellow seed coats produced
seeds with both yellow and green coats. The hybrids must have
carried greenness even though it did not show. There was a split-
ting up, so to speak, of the combined inheritance into its two
components, yellowness and greenness in the seed, or into domi-
nance and recessiveness. This sorting out of members of a pair of
factors is called segregation. This has been found to occur not only
in hybrids but also when pure-breeding varieties are crossed. When
large numbers of offspring of hybrids are considered and tabulated,
the segregation is always in the proportion of one recessive to three
dominants, of which one is pure and two are hybrids.

• •

; x ;

••

fffT

\„ _ _ „ „ mm ./

Black dominates red in cattle. Name the three generations shown in the diagram. Note
also on the sides of the diagram the result of what the animal breeder calls a back cross; i.e.,
hybrid with black and hybrid with red.

326

HEREDITY

When hybrids are crossed with pure dominants, the offspring
will still retain the dominant appearance, but the recessiveness is
not destroyed, for it may be made to reappear in later generations.
These offspring are found to be, approximately, one half pure domi-
nant and one half hybrid, although they may all look dominant.

When hybrids are crossed with pure recessives, segregation again
takes place. One half are recessive and one half appear to be
dominants, but are hybrids. When hybrids are crossed with
hybrids, or with pure dominants, or with pure recessives, the
original parental characters tend to sort out. This, Law of Segre-
gation, is perhaps the most important discovery that Mendel made,
although it grew out of his discovery of dominance.

Problem. What combinations of chromosomes result from maturation
and fertilization f

I. Place two black beans (to indicate chromosomes carrying black color)
in the circle representing the egg mother cell, and two white beans (indicating

mature eg£« Sperms

^mother cell

sperm another cell

the chromosomes carrying white color) in the sperm mother cell. Assume
that the chromosomes have the character-determiners or genes for color only.

A. Move the chromosomes from the primary sex cell to the gametes to
show the change that takes place during maturation (reduction division).

B. Move the beans in the circles representing the sperms, so as to indicate

MENDELIAN LAW OF UNIT CHARACTERS

327

fertilization of the eggs. Show the combinations of chromosomes in the
eggs.

C. Draw in the representations of the chromosomes (beans) . Color the
black and leave the white uncolored. How will you represent the hybrids ?

II. Repeat, the above experiment, using the hybrid combination of chromo-
somes in the primary sex cells. Keep in mind that primary sex cells can be
hybrid in regard to a particular character, but germ cells must be pure,

tncrtwre egg* 6p*rms

•g^nwlher celt \c-^']^~ZL~~\'~^J^'J'^ t,rTn ™>tke£cell
A. Record combinations resulting from fertilizations.

III. Repeat the experiment, using in the male primary sex cell the hybrid
combination, and in the female primary sex cell two recessive white chromo-
somes. Record by means of diagrams, the various possible combinations
resulting from fertilizations.

IV. Repeat the experiment, using hybrid in one cell and dominant black in
the other.

V. What law of heredity did experiment I illustrate ? What law of heredity
did experiments II, III, and IV illustrate?

Mendelian Law of Unit Characters. Another important contri-
bution that Mendel made was his emphasis upon the study of
single characters. In speaking of organisms, the general type is
referred to rather than the individual traits that make up that
type. Fox terrier, for example, or crimson rambler, describes a
complete picture without the need of hundreds of details in which

.328

HEREDITY

that particular variety differs from others. It is known, however,
that the individual organism is a combination of thousands of small

sperm carries

r_J

t—

(

"" : i! "- y

An experimenter, Punnett, devised a method
of predicting how genes combine after crossing.
He used boxes known as Punnett squares.

Turn to diagram on page 321. The gametes
of the parent flowers carry only red, R, or no
color, r. Note in the above diagram, all the
possible combinations of gametes and observe
the identical result Rr — a hybrid.

sperm

carries

T<a& ]

T3-

hyfericl

■Tivbrlcl

r r

Nyhi"te,

The gametes of hybrid, pink four-o'clocks,
carry either the dominant R or the recessive r.
When fertilization occurs, the law of chance
determines whether a pure dominant, a hybrid
or a pure recessive is formed. Notice how the
combinations are described with the Punnett
squares.

differences, some structural,
and some physiological or the
result of physiological activity.
The problem of heredity has to
do with studies in respect to
each of these individual char-
acters.

After Mendel had assured
himself that there was domi-
nance and, later, segregation
for each of several pairs of
characters, he took up the
problem of organisms that dif-
fered in two characters. For
example, some tall plants were
hairy and some were smooth ;
some hairy plants had yellow
seed coats and some had green
seed coats ; some of the yellow
seed coats were wrinkled and
some were smooth. By experi-
ments in crossing for several
generations, Mendel found that
dominance and segregation oc-
curred for each character inde-
pendently of the other charac-
ters, and so he formulated the
Law of Unit Characters.

Simply stated, it means that
a pair of characters behaves in-
dependently of any other pair

MENDELIAN LAW OF UNIT CHARACTERS

329

of characters. This makes it possible to secure various combina-
tions of characters not associated in the original pure stocks. For
example, tallness is dominant to shortness, and yellow seed ~coat
is dominant to green seed coat in peas. If a tall, green seed plant
is crossed with a short, yellow seed plant, the offspring will all be
tall with yellow seeds. Dominants conceal recessives. The fact
that each parent had a dominant and a recessive trait does not
interfere with the laws of heredity which state that the dominant
traits conceal the recessive traits and each pair of characters be-
haves independently. New combinations of characters are thus
set up in the offspring. Offspring do not resemble either parent
in all characters.

Mendel worked eight years on his garden peas and was able, in
1859, to present his results. At that time everybody was excited
about Darwin's work. Few, in fact, none, had time for Mendel.

In this breeding experiment, pigmentation and quality of hair of guinea pigs are the factors
involved. R represents rough hair, r smooth hair ; B denotes black color and b white color or
absence of black. The circles show the genes carried by body cells and matured germ cells.
An animal of the Fi generation carries two pairs of characters and is known as a dihybrid. When
dihybrids are bred, the F 2 generation segregate in the ratio of 9, 3, 3, 1.
WH. FITZ. AD. BIO. — 22

330

' HEREDITY

His paper was received in silence and soon forgotten. In 1900,
sixteen years after his death and thirty-five years after his dis-

BT*

Br-

'Rb

Jot-

BR.
B13

Br-
BR

05b
BR

3otv
BR

Br-

Bt-
Br-

*fcb
Br-

br-
Br-

fcb

Br»
12b

Bt-
12b

"br

BQ
br-

Br
Br-

T3b

Br-

*br-

The Punnett square may be used to show the possible sorting out during maturation of germ
cells of dihybrids and the various combinations resulting after fertilization. Each square repre-
sents an individual. This square shows the possible combinations of genes in the nature of
guinea pigs of different colors and types. The dominant characters are, large B, representing a
pigmented coat, and R, rough hair. The recessive characters are, b, denoting white coat, and
r, smooth hair.

coveries, three other scientists working independently arrived at
the same conclusion. Mendel's work was then given full credit.

Since 1900, it has been proven again and again that heredity is
frequently shown in animals exactly as in Mendel's peas. If pure
black guinea pigs are crossed with pure white guinea pigs, all the
resulting hybrids will be black, showing black to be dominant.

The guinea pig and garden peas show complete dominance.
The Andalusian fowls and four-o'clocks, in which the characters
blend, show incomplete dominance.

Summary. 1. A pure character is one that gives rise only to a
character like itself. The plant or animal possessing it carries pairs
of like factors ; for example, two factors for height, one paternal and
one maternal.

2. A plant or animal is a hybrid when it carries a pair of contrasting
factors. For example, hybrid tall carries both tallness and shortness.

CHROMOSOME THEORY OF INHERITANCE 331

3. Mendelian Laws of Heredity.

a. Law of Dominance. When an individual, which is pure as to
a particular factor, is crossed with another individual which is pure
in the contrasting factor, only one of these factors will appear in
the offspring. The character which appears is called dominant;
the other which is inherited, but is concealed, is called recessive.

b. Law of Segregation.

(1) When hybrids are mated, the contrasting factors are seg-
regated out in the proportion of 25 per cent pure dominant, 50
per cent hybrid, and 25 per cent pure recessive.

(2) When hybrids are mated with pure dominants, there is a
segregation of 50 per cent hybrid and 50 per cent pure dominant.

(3) When hybrids are mated with recessives, there results a
segregation in the proportion of 50 per cent hybrids, 50 per cent
recessives. ,

c. Law of Unit Characters. Every organism contains many pairs
of factors. Each factor, as tallness or shortness, is inherited as a
unit, that is, independently of the other and of any other pair of
characters.

These laws were formulated by the study of the external appear-
ance of the results of different matings. What caused it all? A
difference in the protoplasms of the germ cells has been mentioned.
This is true. Recent investigators have formulated a theory that
has stood the test of much careful checking. The chromosome is
concerned with heredity. It is thought that a certain part of the
chromosome called the gene or character-determiner actually
directs and controls the development of the individual char-
acters.

Chromosome theory of inheritance. If both parents" are pure
as regards a particular character, both the egg and sperm will
contain the determiner for that character and the offspring will
receive a double contribution of the determiner or " gene." For
example, the genes of a pure tall pea plant will carry only tallness ;
the genes in a pure dwarf pea plant will carry only dwarf ness.
The offspring of such pure breds, whether dominant or recessive,
cannot help but be pure. The offspring of the tall plants will be

332 HEREDITY

tall and those of the short will be short. Diagrams similar to
Punnett's (on page 328) may be worked out. Use a capital
" T " for tallness and small " t " (small letter indicates the lack of
dominant character) for dwarfness. The gametes at the top of the
squares are the sperms and those at the side are the eggs. The
combinations in the squares will show the meeting of the chromo-
somes in the fertilized eggs.

Formulae. (1) T X T = TT.

(2) t X t = tt.

When the dominant character is present in one parent only, then
the offspring will have only a single contribution of the gene. The
offspring will appear dominant but will be a hybrid.

Formula. TXt = Tt.

What happens when hybrids are mated? It is believed that
during maturation the contrasting factors of hybrids go into the
separate eggs or sperms. Thus, the male primary sex cell will
be hybrid, but one half of the sperm cells will carry the recessive
factor and one half the dominant. Likewise, half the eggs will
carry a dominant factor and half the recessive. In other words,
the mature germ cells are always pure as regards any one
character. The individual may be a hybrid but the gametes are
never hybrid.

When these gametes of hybrid parents join, the law of proba-
bility shows that the following combinations are possible.
T — >t

Formula. X = TT > Tt > tT > u

z ^ z

When a hybrid is crossed with a dominant, the gametes of the

hybrid will be half dominant and half recessive, while the gametes

of the dominant parent will all carry the dominant gene. The

following combinations are possible.

T — >T
Formula. X — TT. TT. tT, tT

t^T

CHROMOSOME THEORY OF INHERITANCE 333

When a hybrid is crossed with a recessive, the gametes of the

hybrid will be half dominant and half recessive, while the gametes

of the recessive will all carry the recessive gene.

T — >t
Formula. X =T *> Tt > u > u

Results are half recessive and half hybrid.

HEREDITY IN ORGANISMS
Kind of Organism Dominant Character Recessive Character

Wheat Late ripening Early ripening

Wheat Susceptibility to rust Bearded

Barley Beardless Immunity to rust

Maize Round, starchy

kernel Wrinkled, sugary kernel

Cotton Colored lint White lint

Sweet pea Colored flower White flower

Cattle Hornlessness Horns

Rabbits Short fur Angora fur

Mice Pigmented coat White coat

Leghorn chickens . . White plumage Pigmented plumage

Canary Crested head Plain head

Land snail Plain shell Banded shell

Horses Black Chestnut

Bay Black or chestnut

Gray To all colors

Man Curly hair ' Straight hair

Dark hair Light ; red

Brown eyes Blue eyes

Normal pigmentation Albinism
Broad fingers (lack-
ing one joint) .... Normal length

Questions and Suggestions

1. Contrast somatic variations with germinal characters.

2. Diagram, using the Punnett square, the. Andalusian fowls through
two generations.

3. Diagram, using the Punnett square, the Japanese four-o'clocks
through two generations.

334 HEREDITY

4. State and illustrate the three Mendelian Laws.

5. Using a pair of characters in wheat, show how it may breed
through two generations, showing all possible combinations in the
offspring. At the beginning of your Work, be sure to explain the rep-
resentations you use for characters.

6. Using a pair of characters in cattle, show how it may breed
through two generations, showing all possible combinations in the off-
spring.

7. Give a library report on the life and work of Gregor Mendel.

Supplementary Reading

Conklin, Edwin Grant, Heredity and Environment in the Development of Men.

(Princeton University Press).
Guyer, Michael F., Being Well Born; an Introduction to Heredity and Eugenics.

(Bobbs-Merrill Co.).
Journal of Heredity, American Genetic Association. Washington, D. C.
Morgan, Thos. Hunt, The Physical Basis of Heredity. (J. B. Lippincott Co.).
Shull, A. F., Heredity. (McGraw Hill and Co.).
Sinnott, E. W., and Dunn, L. C, Principles of Genetics. (McGraw Hill

Book Co.).
Walter, H. E., Genetics. (The Macmillan Co.).

CHAPTER XXXIV

MUTATIONS

Hugo de Vries.

Keystone View Co.
August Weismann.

What are mutations f What is the importance of mutations f

The theory of germ plasm. August Weismann (1834-1914), a
German biologist, tried to produce a race of tailless mice. He
cut off the tails of tiny baby mice as soon as they were born. When
these grew to adult mice, they mated and had offspring. These
baby mice had long tails. He repeated this experiment generation
after generation. Cutting the tails of the parent mice did not
affect the germ cells of either males or females. He then selected
mice with the shortest of stubby tails, mated them, and continued
to select the shortest-tailed mice for parents. After several genera-
tions of this selecting and mating, a short-tailed race of mice was
produced. He had selected mice whose germ cells carried the gene
for short tails.

As a result of this second experiment, Weismann formulated a
theory explaining why offspring resemble their parents. He
believed that the germ plasm does not arise anew in each organism,
but is actually received from its parents. Explained briefly, his
theory is this : Each new organism begins as a single cell, which is
pure germ plasm. In higher plants, and animals this cell is formed
from the union of an egg and sperm. The cell, called a fertile egg,
begins to divide. Very early in this division, and before differ-

335

336 MUTATIONS

entiation begins, one cell or more will be set aside to produce future
germ cells. . The other cells go on multiplying and form the soma,

er" son* grat^son grecnctson

a piocsm-^,

According to August Weismann germ plasm is derived from the germ plasm of previous
generations. Thus it is continuous from one generation to another. Successive generations
must resemble each other since they are all derived from the same germ plasm. Somatoplasm
develops from germ plasm.

or body cells. From the formei; cells, there develop all the germ
cells of the organism. Germ cells consist of germ plasm, body cells
of somatoplasm. When some of the germ cells of one individual
meet the germ cells of another individual, they will unite, and,
while still in the form of germ plasm, a small portion of it will be set
aside to form the germ cells of the embryo. Thus the germ plasm
is continuous from one generation to the next.

This continuity of germ plasm has actually been demonstrated.
One observer records that when, in a certain worm, the sixteenth
cell stage of the embryo is reached, one cell is set aside to form the
germ plasm and the other fifteen of the cells form somatoplasm.

Mutations. It has already been stated that variations of the
body plasm, which occur during the life of the individual, such as
dwarfing of trees by wind and the acquiring of muscular skill, are
generally considered not inheritable. These are often called
acquired characters. Acquired characters are somatic variations
which are due to environment and are not as a rule transmitted
from parent to offspring. Some experimentation has recently been
undertaken to show that, under certain conditions, acquired char-
acters may be transmitted from parent to offspring. But, since
these abilities were acquired by the soma cells long after the germ

MUTATIONS

337

cell became separated from the body cells, investigators are
having difficulty in explaining how the germ cells can transmit
the acquired characters.

However, a plant or animal will often appear, which, from the
first, is so unlike its parents that it is called a freak or sport. For
example, albino animals which have no pigmentation in fur, skin, or
eyes are not infrequent. White rats have been developed as a
distinct species from a sport which appeared as an offspring of
rats with pigmented coats. Albinism is inherited as a recessive
trait and is sometimes found in humans as well as other animals.
This sudden departure from the ancestral type is called a mutation
and the individual itself is a mutant provided the new species

1st feneration
i8S6-188r

2nSl generation
1898-1889

33l generation
489O-1091

4tk generation.
489S-1896

mxjetccnts

called

parental

type

Oenothera
lamorckiana

15,000

gi£ocS

albi3la:

176

oblon<5bc

rubri "nervis

10,000

i4,0OO

Tiarvella

la-toc

scintillans

Hugo de Vries bred evening primroses through numerous generations. As his experiment
progressed, he observed among them peculiar dwarfed individuals which bred true. He called
these nanella. Then he isolated a type with unusually broad leaves which he called lata, and a
type with reddish veins, the rubrinervis. In successive generations, he observed other plants
with different characteristics. He preserved the new qualities by careful breeding. These
were mutant primroses.

338

MUTATIONS

Cattle originally had long horns. There appeared a mutant without horns. This animal
became the ancestor of a hornless race of cattle.

breeds true to its type. In Paraguay in 1770, there was born a
hornless calf in a herd of ordinary long-horned cattle. Animals
without horns are less dangerous to the other animals of the herd
and also to their owners. Therefore, this animal was later bred
with the ordinary cattle and it was found that the hornlessness
was inherited as a dominant factor. Before this, cattle had some-
times been de-horned, polled artificially, but from this one animal
an entire race of hornless or naturally polled cattle was developed.
The original hornless calf was a mutant.

Short-legged sheep, which cannot jump walls, have been devel-
oped from the long-legged Ancon sheep. Six fingers instead of
five, two joints in the fingers instead of three, and webbed
fingers are a few of the inherited modifications, mutations, that
have been found in human beings. The navel orange (seedless
orange) originated as a mutant in Brazil.

The first person to use the term mutation was Professor Hugo
de Vries of Holland. He was born in 1848 and was, for a long time,
a professor at the University of Amsterdam, Holland. He carefully
watched the descendants of one primrose plant for several genera-
tions and found that it gave rise to seven distinct new species, each
of which bred true. Each mutant differed decidedly from the
others in height, shape of leaves, or some other character.

Mutations are inheritable and there is little doubt that they are

CAUSE OF GERMINAL VARIATIONS

339

due to some germinal variation. They may be dominant or
recessive in character. They are of tremendous economic impor-
tance to man since valuable and desirable mutants can be used lis a
starting point for a new species of plants or animals. De Vries was
the first man to advance the theory that many of our present-day
plants and animals possibly originated as mutants.

Causes of germinal variations. Our ignorance concerning the
causes of germinal variations is profound. We do know that slight
variations are exceedingly common; no two living things, even of the
same species, are exactly alike. Decided variations such as muta-
tions are more rare, but when we become more observant we find
them to be more frequent than, at first, believed. The following
are some of the more common explanations of causes of mutations.

(a) Changes in chromosome number. Scientists found that the
original primrose had 14 chromosomes, but that the 7 mutants
had respectively 15, 16, 20, 22, 24, 27, and 28 chromosomes.
Other observers have also found at times a different number of
chromosomes in other mutants. How or why the number of chro-
mosomes changes is not yet definitely known.

C B

Chromosomes A and B sometimes bend around each other. Before they separate, part of
B becomes joined to A as in C and part of A becomes joined to B as in D. This is called
crossing over. Some of the factors originally in one chromosome are now in the other.

(b) Change in the character of the gene itself. Morgan has found
that most of the fruit fly (Drosophila) mutants that he has studied

340

MUTATIONS

had the same number of chromosomes as their parents. There-
fore, it may be assumed that when the chromosome number does

normal
"Wing

^ r ing
notcK.

vestigial
wing

miniature
wing'

wirier

rudimentary
wing *

truncate

normal
r-<s2i eye

heer*
eye

eyeless
white

T. H. Morgan and his associates have observed the appearance of hundreds of new characters,
mutations, in fruit flies.

change, a mutant is produced, but that germinal variations may
also arise in other ways. Morgan has shown that mutations
sometimes arise as a result of one gene or more actually changing
in character. He has identified over 400 characters which are
carried by the eight chromosomes of the fruit fly (four chromosomes
in each germ cell). He believes that each character is determined
by a gene in a chromosome. Therefore, there are many genes in
each chromosome. Experimental work in heredity makes it seem
highly probable that these tiny units of inheritance are present in
the chromosome, and if they change in character it again seems
plausible that a germinal variation would result.

(c) Crossing-over of genes. Several scientists have done experi-
mental work that would seem to show that sometimes the genes
actually cross over from one chromosome to another. Just be-
fore reduction-division, the chromosomes always arrange them-
selves side by side in pairs. In the fruit fly there would be four

CAUSE OF GERMINAL VARIATIONS

341

pairs. Under the microscope it has been seen that the paired
chromosomes have occasionally exchanged places. This is not a
certainty, because, under the microscope, both members of a pair
of chromosomes look exactly alike. But it can be seen that they
become twisted. The experimental work makes the possibility
seem highly plausible that some of the genes from one chromo-
some of the fruit fly have crossed over to the other.

(d) Decided changes in environment Doctor Tower of the Uni-
versity of Chicago collected 40,000 potato beetles, grouped them
into colonies, put them in glass cages, and subjected them to* varying
degrees of heat and moisture. He found that the change in environ-
ment had no effect upon that generation, but the eggs laid by these
beetles produced offspring of a different color, which continued to

parent

temperature temperature
lov humidity high humility
ydtifaay v v tortuo$<

parent/ jnelanothora^c rubicunaa

Certain scientists are trying to prove that environmental conditions can produce changed
characters in organisms, which will be transmitted to their offspring. Tower subjected parent
potato beetles to certain varied conditions of temperature and humidity. The offspring showed
new characters which they in turn transmitted. Some of Tower's mutants are shown in the
above diagram.

breed true as long as he kept the heat and moisture the same.
Tower has been able to produce mutants by environmental

342 MUTATIONS

changes. Other insects, such as butterflies and grasshoppers, have
been known to produce mutants by a decided change in tempera-
ture, food, and recently by the use of the X-ray. The treatment
of parent fruit flies and mice with X-ray and radium rays has
caused them to produce offspring with somewhat malformed
bodies. These peculiar characters were handed down to the next
generations. The germ plasm had been affected. It would seem
that in some way the germ plasm is affected by the change in
the conditions of the environment, causing mutations to appear
in the second generation. It is not conclusively known whether
a decided change in environment has ever produced mutants in
nature as it has been done under experimental conditions in the
laboratory.

Questions and Suggestions

1. State the doctrine of continuity of germ plasm. How old is
germ plasm?

2. ' What are mutations ? Give examples.

3. What is the relation of mutations to heredity ?

4. What part did Hugo de Vries play in developing the theory of
germ plasm ?

5. Give three theories concerning the causes of mutations.

6. Discuss Professor Morgan's work with fruit flies.

7. Discuss Doctor Tower's work with potato beetles.

8. Give a library report on the biography of August Weismann.

9. Look up in a recent science book or magazine and report on the
experiments that are now being carried on concerning mutations.

CHAPTER XXXV

PLANT

AND ANIMAL

BREEDING

Speed Horse.

Dray Horse.

What are some of the results of plant and animal breeding f What
are some of the methods used by plant and animal breeders to improve
the variety?

Importance of plant and animal breeding. It is only a little
over one hundred years ago that the English clergyman, Malthus,
wrote his famous essay setting forth the principle that population
tends to increase much faster than the supply of food. He believed
that famines, wars, and plagues were useful, at least, in limiting
the population that otherwise would be doomed to slow starvation.

What is the situation to-day ? Since the time of Malthus, the
population of Europe has nearly trebled, and in the United States
it has increased approximately ten times. Yet famines are no
longer experienced except in those countries with poor transporta-
tion facilities. The world as a whole has at no time been so well-
fed nor had so great a variety of foods. Malthus contributed a
fact of real value to mankind in calling attention to the rate of in-
crease of the population. Since that time, modern farm machinery,
good transportation, and knowledge of food preservation have all
aided an increasingly smaller proportion of the people of the world
to provide sufficient food from the farms for the needs of all.

Another factor which has greatly increased the production of
food, and which is of particular interest to the biologist, is the

343

344 PLANT AND ANIMAL BREEDING

improvement of food-producing plants and animals. The cattle
of the Middle Ages were about the size of the average calf of to-day,
but through many generations of selective breeding the size of
cattle and their yield of milk have been increased to a remarkable
degree.

Alfalfa is especially hardy. It withstands droughts, and it may
yield as many as nine cuttings a season. Due to careful selection
of seeds and cultivation of the ground a field of alfalfa will furnish
sufficient food for three to six times the number of cattle which
it formerly supported. Plant breeders have Keen able to increase
the amount of sugar in beets so that the number of pounds of beets
needed to make one pound of sugar has decreased from eighteen
pounds in 1836 to seven pounds in 1904. Luther Burbank im-
proved the potato by making it resistant to a disease called the
potato blight, and by increasing its starch content. It is said,
that this species of potato adds seventeen and one half million
dollars to the farm incomes each year.

One of the best dairy cows of recent years, gave 20,616 pounds
of milk and 1005.9 pounds of butter fat in one year. She gave
more than her weight in milk each month. Contrast this cow with
a prize cow of 1904, that gave 567 pounds of butter fat in one
year.

Every day our agricultural experiment experts and other scien-
tists are improving our foods. These products are not produced
in a haphazard way. They are frequently the results of careful
experimental breeding. It is, however, only within the last
twenty-five years that sufficient knowledge of the laws of heredity
has been available to put plant and animal breeding on a scientific
basis.

It is the plant breeders concern to increase the food content of
grains and fruits, to produce new species immune to disease, to make
certain varieties hardy so that they can be grown in more northern
climates, and to hasten maturity. The average yield per acre

IMMUNITY TO DISEASE

345

of wheat was between 10 and 15 bushels per acre. By selection and
cultivation, the yield per acre has been increased to over 40
bushels. - Wheat has been bred so that several species now combine
the desirable qualities of large yield per acre, good quality for
bread making, hardiness, resistance to rust, and resistance to
drought. The ordinary corn stalk usually produces but two or
three ears. But through experimentation, corn has been produced
with stalks 16 feet high and which bears 32 ears to the stalk.

The particular aims of plant and animal breeding are to
establish varieties immune to disease, to produce new species, to
breed for desirable characters, to improve quality by proper selec-
tion and to make both old and new forms more productive.

Immunity to disease. In some of the Southern States, the
cattle had long been subject to Texas fever which was easily
spread and caused the loss of
many cattle. It was learned
that the wild Brahmin cattle of
India were immune to the dis-
ease. Their jlesh, however,
was not valuable as beef. Two
strains, our southern cattle
and the wild Brahmin, were
crossed. Immunity to Texas
fever was found to be domi-
nant in the Fi generation.
These hybrids were mated
again and from the F 2 genera-
tion only the immune animals
that seemed to show the best
beef tendencies were selected
and bred. By careful selection
a species of cattle combining both immunity and good beef
qualities was thus obtained.

WH. FITZ. AD. BIO. — 23

U. S. Devi. of Agric.
Animal breeders have produced from the orig-
inal wild strain of pig shown above the fine
specimen shown below. Compare the food value
of the two specimens.

An average dairy cow gives approximately 8304 lbs. of milk per year containing from 130 to
300 lbs. of butter fat. The daughters of a famous sire, Fauvic's Prince, averaged 17,135 lbs.
of milk per year. Their average yield of butter fat is 801 lbs. per year. Fauvic Star, the middle
cow on the right broke all records with 30,616 lbs. of milk and 1005.9 lbs. of butter fat.

346

PRODUCTION OF NEW SPECIES

* 347

A certain fungus disease in wheat is recessive. In 1906, from
a field of badly infected wheat in Kansas, a lone plant was dis-
covered that showed no signs of rust. This single stalk was
probably a mutant. It was tested, propagated, and the offspring
were carefully selected for immunity as well as for the desirable
qualities of the parent
wheat. An immune spe-
cies that also gave an' in-
creased average yield of
four and one half bushels
per acre was finally pro-
duced. In 1917, this strain
of wheat, called Kanred (a
combination of Kansas and
its color — red), was dis-
tributed for commercial
use and has already in-
creased the wheat income
in Kansas by many million
dollars per year. The
same procedure was fol-
lowed in combating a
blight that often affected
corn.

An immense amount of
damage is annually done
by corn smut. Some
sound ears were found in fields of corn that were badly infested
with corn smut. The sound ears were selected and bred until an
immune variety was obtained.

Production of new species. A white blackberry sounds like
a paradox, but we use the term in referring to a new blackberry
developed by Luther Burbank. He noticed a wild fruit, bitter,

Underwood & Underwood
Corn has been improved through careful breeding.
Desirable characters such as number of kernels, food
content of kernels, regularity of formation of kernels
and size of ear have been combined in the same corn
plant. A prize red corn of Kansas is shown in the
picture.

348 PLANT AND ANIMAL BREEDING

small, and really a light yellow rather than white. It was, without
a doubt, a member of the blackberry family. He hybridized this
by crossing it with the Lawton blackberry which was black, large,
juicy, and of pleasing flavor. He found that black was dominant
over the light yellow. In the F2 generation the light color again
appeared, and by selecting for several generations only the plants
for breeding that combined the lack of color with the desirable
flavor and size, he obtained a large tasty berry that is now known
as a white blackberry.

Some varieties of plants have been improved in many different
ways. Luther Burbank studied various kinds of plums obtainable
here and in other countries. He crossed American, Japanese, and
European kinds. Then he selected the best for further experi-
mentation. As a result, he obtained different species : (1) of
many varieties in the coloring of skin and the texture of flesh;
(2) of a wide variety of shapes; (3) of a wide variety of new
flavors and aromas ; (4) of sizes that are increased to three inches
in length and two and one half in diameter; (5) that produced
either early or late species. (Some ripen a month before the
earliest of the old varieties; others ripen as late as December.)
(6) that are not affected by the frost or cold weather. Some
plums have been developed that can be shipped long distances
without spoiling. A species has been produced that can remain
on the tree a month or two in hot weather without decaying,
unlike the old varieties which had to be picked as soon as they
were ripe. Some trees bearing these new varieties will begin
to bear abundantly the third year if cuttings from young trees are
grafted upon trees of ordinary size.

Some of these new plums grow in climates and under conditions
where the plum has hitherto been a failure. The Beach plum is a
wild species growing along the coast. It is a low, spreading shrub
with a small bitter fruit. It is very prolific and is resistant to cold
and frost. This was crossed with an American plum. The result-

BREEDING FOR POINTS

349

ing species, called the Im-
proved Beach plum, bears
very abundantly. It is a de-
licious plum, of very fine flavor
and with a small stone. It is
indifferent to frost, and bears
under the most trying condi-
tions of soil and climate.

A cross between a plum and
apricot has been produced by
Luther Burbank. It is called
the plumcot. He also pro-
duced a stoneless plum.

Breeding for points. Seed-
lessness has sometimes devel-
oped as a mutation. The
seedless navel orange origi-
nated as a mutant in Brazil.
Twigs from it were grafted on
to ordinary orange seedlings.
Two of these tiny plants
thrived, and from them, prop-
agated by grafting, all of the
navel oranges have been pro-
duced. The value of vegeta-
tive' reproduction as a means
of making a new species breed
true to type is very great.
Since this makes use of the
body plasm, it will continue
to produce other plants like
itself. For instance, if a breeder has produced a large, double-
petaled, red-flowered dahlia, he may be sure that the bulbs of this

The Lawton blackberry.

The white blackberry that was crossed with
the Lawton blackberry.

350 PLANT AND ANIMAL BREEDING

dahlia will give rise to large double blossoms colored red. If he
plants the seeds, however, he will probably find outcroppings of
the plant's ancestry in the way of small flowers, some single rather
than double, some with white petals, and so on. The potato at
present rarely bears seeds. When such seeds appear and are
planted, different kinds of potato plants may result. Many of
these plants may bear potatoes that are small, irregular in shape,
and low in food content. They closely resemble their wild an-
cestors. Therefore, the potato is propagated vegetatively by
using parts of the tuber containing the " eyes." Tomatoes were
formerly small, tasteless, and full of seeds. But through selec-
tion and cultivation, many splendid varieties have been developed,
within the last generation. Other details that have been brought
out through breeding are : increased egg laying in hens, increased
milk supply from cows, and increased starch and protein produc-
tion in corn.

Improved quality. The southeastern region of the state of
Washington was an excellent locality for growing wheat. But
the climate is so severe that every three or four years, the entire
crop was killed by frost. The problem of producing a hardy
variety of wheat was turned over to Mr. Spillman of the United
States Department of Agriculture. He selected as a beginning,
the Little Club wheat, named for the short, clublike appearance
of the head. It was desirable because it had a stem strong enough
to resist storms and a head that remained closed long after ripen-
ing. Thus the ripe grain was protected and was not likely to be
lost before harvesting. This species was crossed with other varie-
ties, including a hardy winter variety that would resist frosts.
After ten years of careful selection and propagation, an improved
frost-resistant variety of Club Wheat was obtained, that is now
grown in the extreme Northwest. Winter character was found
to be dominant over spring character and the club head to domi-
nate over long head.

INCREASED PRODUCTION

351

This white leghorn hen established a record by
laying 321 eggs in 51 weeks.

Increased production. In
almost all plants and food
animals, a great increase in
production has been brought
about and there is still room
for much improvement.
Careful selection of the best
types for breeding is a very im-
portant factor here. Burbank
increased the food content of
the potato by 25 per cent ;
Kanred wheat, merely through
vigilant selection of the most
productive plants for seed, sur-
passed its parent wheat by an
increased yield per acre. The
average cow's milk will pro-
duce 125 pounds of butter per
year, but a Jersey cow will
usually produce over 1000
pounds of butter in a year.
A 300-acre field in southern
Illinois was planted with im-
proved corn and yielded 30
bushels more per acre than
the fields planted with the
ordinary seed.

Methods of breeding.
Hybridization is the crossing of
two individuals carrying unlike
characters. This has the ad-
vantage of combining the desirable characters found in the two
individuals into one individual.

This barred Plymouth Rock hen laid 287 eggs
in a year. The American egg record for three
consecutive years was 282 eggs and 281 eggs
made by two Barred Plymouth Rocks, and 303
eggs from a hen which was a cross between a
white leghorn and a Barred Plymouth Rock.

352 PLANT AND ANIMAL BREEDING

Artificial selection. Many experiments in breeding start with
hybridization, but they would be of little value unless the indi-
viduals showing undesirable traits were disregarded and only those
showing the desirable characters kept for breeding. This is called
artificial selection. Even so, the organisms showing the useful
traits will oftentimes not breed true as they are hybrids. To be
successful and establish the desirable qualities, large numbers of
matings must be tried out and only those that breed true should be
retained. As has been said before, when vegetative propagation
is possible, it is a certain means of breeding the plant true to type.
Improved kinds of fruit trees are propagated only by grafting.

Method of plant propagation. The typical method of plant
propagation was that used by Burbank. The flowers which are to
furnish the pollen are carefully gathered a day or so beforehand.
The pollen is sifted from the flowers and kept in a cool place. The
tree to which the pollen is to be applied is deprived of most of its
blossoms in order that the remainder may be sure to develop and
that there may not be too many to be properly looked after. The
buds of the remaining blossoms are prepared for artificial pollina-
tion by cutting away the petals and the .attached stamens. The
pistils and stigmas are left uninjured and are protected from in-
sects. Since there are no brightly colored petals to attract them, or
anything for them to hold on to when entering, bees seldom ap-
proach these flowers. If there is any danger of insects visiting

the flowers, a paper bag is fre-
quently tied over each individ-
ual flower. When the pistil
ripens, the pollen is applied by
dipping a brush or finger into
this yellow powder and touch-

aae^h American ^^ ing the stigmas. All of the

pixxm. plw«w best seedg that develop from

The size, flavor, and quality of plums have been . . . . .. ,

improved through selection and cultivation. tne truit 01 the pistil tUUS

- METHODS OF ANIMAL PROPAGATION

353

treated, are saved and planted. When these new plants produce
fruit, only the best seeds are selected. Frequently, the young
plants are grafted upon other
trees to hasten the growth. Hy-
bridization is but the beginning
of breeding. Careful selection
must be continued, so that a pure
type is established.

Methods of animal propaga-
tion. If a mutant with a desir-
able character is found, it is bred.
In case the new character is dom-
inant, it will appear in the Fi
generation, but the animal of this
generation will be hybrid. This
hybrid is then mated with an
animal which shows the same
desired character. Sufficient
matings must be made to get
the character in a pure form.
This sometimes necessitates close
breeding. By close breeding is
meant mating individuals closely
related, as grandparent with off-
spring of the second, third, or
succeeding generations. The fact
that animals frequently take a number of years to mature is
a serious difficulty met with in animal breeding. Close breed-
ing does not necessarily reduce the vigor, but, if there are unde-
sirable characters present, they may be doubled and the offspring,
then, cannot be used for breeding purposes. In case the new
character is recessive it will not appear until the F 2 generation.
Then, if two individuals of different sex of this generation pos-

The Beach plum grows in clusters. It is a
small plum, smaller than the American plum.
When these two plums are crossed, an im-
proved plum, much larger than either parent,
is produced growing in bunches, like the
parent Beach plum.

354 PLANT AND ANIMAL BREEDING

sess the desired characters, and are mated, their offspring will
usually be a pure type.

Questions and Suggestions

1. What bearing has plant and animal breeding on the food situa-
tion of the world ?

2. Why is scientific plant and animal breeding a comparatively
recent development?

3. State five aims of plant and animal breeders.

4. Describe in detail an example of each aim mentioned in
question 3.

5. Describe in detail how a particular trait may be established.

6. What two biological principles are involved in breeding experi-
ments ?

7. State three difficulties animal breeders encounter that are not
encountered by plant breeders.

8. Look up and report on the life and work of Luther Burbank.

Supplementary Readings

Osterhout, W. S. V., Experiments with Plants (The Macmillan Co.).
Sinnott & Dunn, Principles of Genetics (McGraw-Hill Book Co.).

CHAPTER XXXVI

EUGENICS

Sir Francis Galton.

Underwood & Underwood.
Charles Davenport.

What is the importance of eugenics f What is the difference between
eugenics and euthenicsf How can eugenics and euthenics be applied
practically f

Eugenics is the division of biology that deals with the improve-
ment of the human race. It is a new science built upon an applica-
tion of what we know concerning the laws of heredity. It also
includes the study of how to improve the environment, although
the effect of environmental conditions on people is frequently
referred to as euthenics.

History of the eugenics movement. In 1883, Sir Francis Galton,
an Englishman, became interested in the science concerned with
the improvement of the human race, to which he gave the name
eugenics. He had in mind the improvement of human character-
istics through heredity. In 1921, the Second International Con-
gress of Eugenics stated that eugenics was the self-direction of
human evolution. This means that individuals through good or
poor marriages, can improve or impair the mental or physical heri-
tage of future generations. The science of heredity has contrib-
uted much to eugenics. Many family histories have been inves-
tigated and different physical and mental traits have been traced
through generations, with the utmost care. These investiga-

355

356

EUGENICS

tions have given data for the practical applications of eugenics. An
Eugenics Laboratory is located at Cold Spring Harbor, Long Island,
under the supervision of Dr. Charles B. Davenport. Research in
the science is being carried on there by the most careful specialists.
Methods of investigation. — Families of superior ability.
Human heredity has not been studied by the experimental method
as successfully as animal and plant heredity have been stu.di|df
There are three reasons for this failure : (1) The length of life Bso
long that no investigator can live long enough to study, personally,
the heredity of more than two, three, or possibly four generations
of a family ; (2) the number of offspring is small and it is difficult to
draw valid conclusions from the limited data offered ; and (3) our

□ o

male female

^marriage line

4r- ciescent line

■T~j s. parents

dtitid

t^in.s

"Koman figures
cct left inciicate
gene r-at ion^

s l=<iViIaren-

**L.lnf

^B.ie3L in.
infcmc^

Arabic figures
locate ^
xnd.iv i cltf ccl jS

m. q

alcoholic blin2L d>af epileptic feSS^L insane normal jtubeaallar

The Eugenics Record Office at Cold Spring Harbor has adopted a standard set of symbols

used in chart making.

social customs handicap the work in this research, as people con-
sider family affairs private and will not give information freely.

METHODS OF INVESTIGATION 357

Sir Francis Galton applied the statistical method to the study
of heredity in human beings. By this system, the pedigrees of
many families have been traced for generations and studied lis a
means of determining what traits seem to occur most frequently
in a majority of the descendants. Such a study has been made of
the family of Jonathan Edwards. He was born in 1703 and was
noted for his strength of character and for his high mental ability.
In 1900, 1394 of the descendants of Jonathan Edwards had been
traced and the life work of many of them discovered. They
included many college presidents, professors, lawyers, doctors, able
business men, and state officials. The group as a whole was
highly intelligent and capable, with a high sense of civic respon-
sibility. Their historian states that it is not known that any of
them were criminals. The Edward family indicates that high
mental ability is inheritable.

An investigator recently tested a number of children for intelli-
gence. Forty-one showed superior intelligence. What of their
immediate ancestors? Of the forty-one, the investigators found
that only two lacked a near relative with a superior intelligence
rating. Definite talent in some form was found in different
members of the families of these children. A study has been pub-
lished concerning the intelligence of some students of Oxford Uni-
versity, , England. The records of boys who secured marks of
" honor " and " pass " were compared with the records made by
their fathers. Of the " pass " students only twenty per cent of
the fathers had taken first or second honors. That means they,
too, were only in the " pass " class in their school days. On the
other hand, of the students taking first honors, nearly forty-two
per cent of the fathers had taken first or second honors.

Woods has made, a study of several royal families, in which a
comparison is made between parents and offspring in mental and
moral qualities. There is a very marked similarity and uniformity
shown in the results of this study. A resemblance between

358 . EUGENICS

grandparents and 'grandchildren is evident though not as notice-
able as closer relationships. Outstanding groups of individuals
have descended from Peter the Great of Russia, William the Silent
of Holland, Isabella of Spain, and Gustavus Adolphus of Sweden.
Th3se studies have shown that men of the type of the Sidneys,
Balfours, Cecils, and Churchills in England, and the Lowells,
Eliots, and Dwights in America are not the result of chance or
accident, but that their superior abilities are inheritable traits.
When an exceptional man chooses an exceptional wife, the ma-
jority, if not all, of their children will probably be exceptional. All
members of royal families are not superior. There are some groups
that show insanity, imbecility, and other mental defects, because
these traits have been introduced through marriages with mental
defectives.

There seems little doubt that a certain stock or family will pro-
duce men of great ability more frequently than will another stock
or family. It is almost certain that the quality of mind and body of
the parents will affect the offspring. Parents, sound in mind and
healthy in body, tend to produce normal healthy children.

Families of inferior ability. Parents physically weak and of a
low-grade mentality will give to the world undesirable progeny,
probably physically unfit and with mediocre intelligence. An
American family which has been given the fictitious name of
" Juke " has been carefully traced through a large number of
generations. This family record starts with a shiftless vagabond
born in New York state in 1720. In 1915, students had traced
2094 members of this family: 1600 were feeble-minded or epi-
leptic, 310 were paupers, 140 were convicted criminals, and large
numbers of the remaining group were traced through the records
kept in workhouses and other public institutions. This family by
1915, had already cost the state of New York more than $2,500,000
and the expense still goes on. Their descendants will continue to
bear the same traits. The mental ability of this family is very

FAMILIES OF INFERIOR ABILITY

359

low. Only twenty have been known to learn a trade and ten of
these did so while in state prisons.

The story of the Juke family indicates that weakness of char-
acter and low mental ability will give rise to offspring with little
moral or mental stability. Although this study does not prove
that a tendency toward wrong-doing is inheritable, it certainly
does show, at least, that weak character and low mental ability
give rise to a person who often becomes a .criminal. The Jukes
lack the judgment, memory, and will power that enable people to
fulfill responsibilities toward their fellow men.

The Kallikak family (the name is fictitious) throws still more
light on human heredity. Martin Kallikak, a normal, healthy

feeble min&eSL mother

Intelligence and lack of intelligence seem to be inherited characters. One of the lines of
descent of Martin Kallikak shows feeble-mindedness inherited from a feeble-minded mother.
Of 480 descendants studied, only 46 were known to be normal. The other line of 496 descend-
ants from Martin Kallikak and a normal wife was practically all normal.

young soldier who fought in the American Revolution, had a son
by a feeble-minded girl. This son had a family of ten children from

360 * EUGENICS

whom there are 480 known descendants. Of these, only 46 are
known to have been normal while 143 were feeble-minded. Knowl-
edge concerning the others is missing or doubtful. After the war,
this same soldier, Martin Kallikak, married a normal woman.
From this union there have been 496 descendants ; none of whom
were feeble-minded. The history of the Kallikak family indicates
that feeble-mindedness is inheritable. The defective descendants
were incapable of earning a living and some could not provide for
themselves nor care for their physical comfort. It is necessary
that these defectives be fed and sheltered, but it is more impor-
tant that they be segregated in institutions where they cannot
produce more offspring like themselves.

The number of mental defectives in England and Ireland has
been estimated to be about five per cent of the population. In
1923, in the United States there about 267,600 mental defectives.
The annual cost of caring for these persons was nearly $80,000,000,
to which should be added three hundred millions of dollars which
was the corresponding loss in industrial activity of these depend-
ent people. In some states, one eighth of the total state expen-
ditures is for the care of the insane.

The cost of crime in the United States is ten billion dollars an-
nually. Over twenty per cent of the inmates of jails, almshouses,
and other institutions are foreign-born, although only fourteen per
cent of the total population is foreign-born. There seems to be
twice the number of foreign-born as native-born among the defec-
tive group which includes the feeble-minded, insane, epileptics,
criminals, blind, deaf, paupers, and other dependents on a com-
munity. This is probably due to the fact that many foreigners
of poor stock were formerly admitted to this country, but such
undesirable aliens are now excluded. Therefore, the above figures
include the people admitted before our immigration laws were so
strict. They also show the necessity of a careful physical and
mental examination of all immigrants to this country.

FAMILIES OF INFERIOR ABILITY 361

A study of the records of 447 criminals showed that among
their parents, 10 per cent were criminals, 6 per cent were victims

Key

■ boat
design.

W artistic

W\ musical
P -mechanical
fl litemr^
I 1 normal

x So^o5i5ip5i|Oio

The Herreshoff family is noted for special skill in boat designing and building. Many cup
winners have come from their yards, some of which have competed with Sir Thomas Lipton,
challenger. The above chart includes one line of descent of the family. The entire genealogy
has been traced and is recorded in the Eugenics Record Office at Cold Spring Harbor.

of hysteria, 4 per cent of epilepsy, 15 per cent of alcoholism, and
9 per cent of insanity. In a study of the inmates of certain
penal institutions, 20 to 30 per cent were found to be mentally
subnormal. Some, however, were normal and some very keen.
Yet crime and mental deficiency are usually closely related. A
criminal type, as such, does not exist. When people of low in-
telligence are trying to fill positions which put too great a demand
on their mental ability, they frequently lose their positions. Not
understanding the cause, and, in some cases, being unable to get
work, they remain idle. This makes them desperate and fre-
quently leads them into bad and vicious company. When low
intelligence is combined with emotional instability, the unfortu-
nate persons frequently become wayward and turn to crime.

From these and similar investigations it has been ascertained
that desirable traits in man, such as high intelligence, without

WH. FITZ. AD. BIO. — 24

362 EUGENICS

which we cannot develop will power, self-control, or a high moral
responsibility, are inherited. Other studies indicate that special
aptitudes such as musical or artistic ability as well as mathema-
tical and inventive aptitudes, literary ability, and retentive mem-
ory are inherited. On the other hand, a startling number of
feeble-minded people and those of low mentality are responsible
for the large criminal and defective groups that fill our chari-
table and public institutions.

Race improvement. There are two ways of improving mankind.
This improvement may be called " human conservation." One
method of bettering the race consists in giving every child the best
possible inheritance. This is eugenics. This requires thought-
fulness in selecting a mate so that the children will have desirable
traits. Another method is to improve the environment of every
individual and to give him the best possible opportunity to develop
his capacities. It is true that anything which safeguards the
health of the present generation also helps to safeguard the next.
This second method is euthenics. It might be called the science
of learning to live well. It consists of an endeavor to improve
the individual through improving his environment and his training.
If all people understood and practiced eugenics — being well born
— and euthenics — living well — the world would be greatly im-
proved.

The Eugenics Laboratory has collected many valuable statistics
and data on human heredity. Research work is continually going
on. If a man and woman contemplate marriage and question
the possibility of some undesirable trait in one or both of the
families being transmitted, the Eugenics Laboratory will give
an opinion on the desirability of the marriage. For instance, if
there is a tendency to deafness in one of the families, with perhaps
some members being deaf mutes, there would be a double possi-
bility of the children inheriting deafness if the family of the other
prospective parent had the same trait, even though in a milder

SUGGESTIONS FOR RACE IMPROVEMENT 363

form. In some states marriages of first cousins are prohibited
by law. The biological reason for this is made clear by the ex-
ample above. If an undesirable trait runs in a family, both
parents would be likely to carry it and there would be a double
possibility of their children inheriting it.

Suggestions for race improvement. (1) Segregation of the
feeble-minded and prevention of their marrying are obvious
methods for eliminating defectives and increasing the mentality
of society as a group. Most states support such people in insti-
tutions. This is a very costly method. A method that shows
great promise is the colony system used in some parts of New
Jersey. The mental defectives are kept in colonies, the men sep-
arate from the women. They are all taught trades, and may
travel in groups through the state under the strict supervision of
guards. They do some road building, farming, and simple tasks
which are parts of other industries and require little intelligence.
In this way they earn money and help to maintain themselves.

(2) As far as possible, the insane, criminal, and diseased should
also be prevented from marrying. If they could be kept in in-
stitutions, and have no offspring, the number of defectives in the
succeeding generations would be gradually diminished.

(3) All people should have an understanding of the value of
eugenics. This is made possible by teaching pupils in high schools
and colleges, the part played by inheritance in the life of
every one, and to what extent certain characteristics or tendencies
may be inherited. An enlightened public consciousness must be
developed all through the world, if racial progress is to be made.

(4) Certain laws in relation to marriage might be enacted and
enforced. Each person desiring to marry should be compelled by
law to pass a physical examination to determine whether he is phys-
ically fit, or whether he possesses certain defects that would make it
unwise for him, from an eugenic point of view, to marry and prob-
ably pass on these disabilities. Some states already have such

364 EUGENICS

laws in operation. Wisconsin has enforced such a law since 1914.
In this state the people show an intelligent interest in their health.
Before any man may receive a license to marry, he must have a
thorough health examination. If an applicant for a marriage
license is told that he has a disease which makes it unwise for
the marriage to take place, in most cases such a person is interested
in learning how to overcome the handicap so that he may marry
at some future time. The enforcement of this law is having a
beneficial effect on the health of the people, as a whole, and it cer-
tainly will mean better health for the next generation. When
such laws are in operation, only the fittest are selected for parent-
hood.

(5) The environment may be improved by enacting and enforc-
ing laws concerning :

(a) The eight-hour day

(b) Better tenement and housing conditions

(d) Compulsory education

(e) Laborers' compensation laws
.(f)- Widows' pensions

(g) Child Labor laws '

(h) Vocational guidance and training

The eight-hour day permits a man to live a normal life with
sufficient opportunity for education, recreation, and physical re-
laxation. Better tenement and housing conditions will give all
children opportunities to grow up in a clean, wholesome environ-
ment. All houses should be built so that fresh air, sunlight, and
good sanitation will be available for every person, no matter how
rich or poor he may be. Public playgrounds for children will
prevent accidents that kill and maim so many children who have
no place to play except the streets.

The compulsory education laws vary in the United States. Most

SUGGESTIONS FOR RACE IMPROVEMENT

365

of them insist- that all boys and girls remain in school until they
are at least fourteen years old or have the equivalent of six years
of schooling. But, in some sections of the country, these laws^are
not enforced at all, while in other sections boys and girls are re-
quired to remain in school until they are seventeen years of age or
have graduated from a secondary school. The schools are the
medium through which the home and the community are edu-
cated. They are a direct means of raising the standards of living
all through the country. Schools are also the most efficient means
of ridding people of unhygienic racial and social customs.

Many state compensation laws guarantee that a man's family
will be cared for in case he meets with an accident. Even though
this compensation may be small, it is of some value in helping to

Brown tiros.
A typical group of immigrants at Ellis Island awaiting admission to the United States.

maintain a good or at least a decent environment for the family of
such a person.

In various states, laws have been enacted which provide pensions

366

EUGENICS

for widows who are in need. Some of these laws even provide for
orphans up to the age of fourteen or of eighteen years of age. The
average grant usually varies from one hundred to two hundred

dollars per year for each
child. In many cases,
the law demands that
the mother be a fit per-
son physically, mentally,
and morally, if she is to
receive the pension
which enables her to keep
her children with her.

Previous to the intro-
duction of the modern
factory system in the
eighteenth century, chil-
dren were commonly em-
ployed in factories.
Authorities of pauper
institutions in Great
Britain permitted pauper
children to work as much as sixteen hours a day. In 1847, the
hours for child laborers were reduced to ten hours a day. To-day,
in most states of the United States a boy or girl may leave school
at the age of fourteen and obtain working papers. In many
states this is conditioned on the passing of a health examination.
Five states of the United States are said to furnish one third of
the total child laborers and one half of all child illiterates in the
country. Congress has twice tried to pass laws regulating child
labor but each time the law has been declared unconstitutional.
In order for children to develop physically and mentally to the
fullest extent, it would be wise to keep them out of factories and in
school with suitable childhood recreation until, at least, the age of

Immigrants are examined at Ellis Island to make sure
that they are physically and mentally fit. All those
suffering from mental disorders or from contagious dis-
eases or who are, otherwise, physically unfit to make re-
sponsible citizens are excluded from the country.

SUGGESTIONS FOR RACE IMPROVEMENT 367

fourteen. In some European countries, children under eighteen
are not permitted to work at night or at hazardous trades. In
many of our states the minimal age for hazardous trades such as
quarrying and mining is sixteen. There is agitation in many
states to keep boys and girls in school until the age of seventeen.
They will then stand a better chance to enter industry with a
fairly good physical and mental equipment.

Vocational guidance and training are invaluable in directing chil-
dren into vocations for which their intelligence seem to fit them.
When properly directed, people with superior intelligence should
be able to get established earlier than they usually do. Less gifted
children should be advised to do that type of work which they can
do rather successfully. This will give them a feeling of satisfac-
tion in their work, which will make for contentment and happiness
When people are continually losing their jobs, due to their inability
to perform the tasks given, idle and vicious habits usually result.
Continuation and trade schools are invaluable aids in teaching chil-
dren trades. Such trained children, naturally, tend to be better
citizens and better tradespeople. Special classes have been de-
signed for children who are disinterested and unable to keep up
with the work of the regular classes. Another type of school called
the juvenile vocational school, designed to meet the needs of such
children, is now being established in certain sections of the country.
Not only will children who cannot get along well in the average
public school attend these schools, but those who, due to economic
pressure, must earn a living as soon as possible, will find a place to
learn a trade.

(6) Only the mentally, physically, and morally fit immigrants
should be permitted to enter other countries. At present there
are immigration laws restricting certain undesirable persons. Im-
migrants are examined when they leave their own country, and
at Ellis Island before* entering the United States. Care is taken
to exclude all those with objectionable hereditary traits or with

368 EUGENICS

contagious diseases. But the effective enforcement of these laws
is still a serious problem.

Eugenics versus euthenics. Environment and heredity must
go hand in hand if real racial progress is to be made. Bad en-
vironment may harmfully affect good germ plasm. Frequency
of crime is sometimes laid to environment rather than heredity.
This is true to some extent, but heredity is usually responsible for
choosing the environment. Intelligent people, as a rule, wish to
live in good surroundings where they will meet people like them-
selves. They try to meet and solve their problems. Subnormal
people are frequently content with poor conditionSvof Kymg. Lack-
ing normal will power and the ability to solve tnen problems in-
telligently, they are dominated by the wrong influences. It is
very difficult to dissociate, absolutely, heredity and environment.
There is no question about the fact that eye color, hair color, and
other structural characteristics are inherited, but there is little
known about the inheritance of emotional characteristics.

Inheritance of disease. It is a fairly well-established fact that
no germ disease is inherited. In order to be inherited, a microor-
ganism would have to become a part of a gene in the chromosome.
Since this is impossible, germ diseases are not really inherited al-
though infection may occur at birth, so that the effect on the new
individual is the same as direct inheritance. In all probability,
organic diseases, like malformations of glands, deafness due to
structural defects in the ears, and organic heart disorders due to
structural defects in the heart, do run through families. Weak-
nesses in various organs may be inherited and result in tendencies
or predispositions toward disease.

Any disease of the mother, that gives off poisons that will circu-
late in the blood may affect the germ cells and result in some ab-
normal development of the unborn offspring. Such children may
be born crippled, blind, deaf, or mute. Any disease of the mother
that interferes with the nutrition of the unborn child may also

INHERITANCE OF DISEASE 369

cause developmental defects. For example, the offspring of a
tubercular mother is likely to be delicate, lack resistance to dis-
ease, or may show definite defects, because of faulty nutrition.
The toxic and nutritional effects on the offspring are due to its
environment. In these cases the environment is the mother's
body. The relation is called intramaternal environment in con-
trast with the environment of the child after it is born. This
is called extramaternal environment.

The relation of alcoholism to the offspring is not conclusively
established. Experiments are constantly being conducted to
determine whether alcohol may modify the germ cells or not. It
is a fact that children of drunkards are frequently defective. This
defectiveness may be (1) due to the fact that alcoholism is merely
a symptom of a degenerate stock. In this case the children will
be defective, not because their parents drank, but because their
parents were defective. The parents' drinking is merely one of
the symptoms of their defectiveness. (2) It may be that alcohol
directly poisons the germ plasm. In this case parents of sound
stock, who become addicted to alcoholism, will have defective off-
spring. (3) It may be that the intemperate parents do not take
adequate care of their children and this leads to the defects of the
children. Whether the tendency for drinking alcoholic liquors
is inherited, has not yet been definitely proved.

Environment versus Heredity. One of the most interesting
studies that has been conducted upon the relation of environment
to heredity in the life of a child is the investigation of identical
twins. Twins are thought to originate in the following way. When
a fertilized egg divides into two cells, some mechanical or chemical
difficulty may separate one cell from the other. Then each cell
develops separately. The development of the two cells is exactly
alike in every particular because each cell resulted from the
division of the original cell. Such a development results in twins
identical in sex, height, coloring, and almost every other particular.

370

EUGENICS

Investigators have found a pair of identical twins that had been
separated at infancy and had been brought up in different envi-

Journal of Heredity
These identical twins were separated in their infancy. They were tested, after seventeen
years of separation, and found to be very similar in physical and mental characteristics.

ronments in different families in, approximately, the same social
conditions. When they became adults, they were given intelligence
tests and both were found to have practically the same intelligence
quotients. They were successfully occupying professional posi-
tions requiring about the same intelligence. The different envi-
ronments had produced little change in the inherited mental
abilities.

Questions and Suggestions

1. What is eugenics ? Give the history of the science of eugenics.

2. What are three difficulties in investigating human heredity ?

3. Discuss how histories were obtained from families of superior
intelligence; from families of inferior intelligence.

4. What is the relation of crime to heredity ?

5. State two general methods of race improvement.

6. Name seven euthenical measures that may be enforced ; discuss
their importance.

7. Discuss the topic "Environment versus Heredity."

CHAPTER XXXVII

PROGRESSIVE
DEVELOPMENT

Jean Lamarck.

uruwn Bros.
Charles Darwin.

How has organic evolution of plants and animals taken place f How
old is the earth? How old is man? What are some of the evidences
of evolution f

All plants and animals of to-day are thought to be descendants
of earlier and more primitive types. Organic evolution is the
science that deals with the origins of species and the changes in
them from generation to' generation. Evolutionists believe two
things: (1) that individuals of the same species always vary;
and, (2) that many of these new characteristics or variations are
transmitted to succeeding generations. Heredity is, therefore, one
of the cornerstones of evolution.

History of evolution. Aristotle had an idea that there had been
a gradual succession of living things from the simplest animal to
man, but this supposition was unsupported by evidence or fact.
He had seen the remains or parts of plants and animals in rock.
To-day these are called fossils. He thought they were examples of
spontaneous generation taking place in the depths of the earth
and that such forms never had a chance to live on the surface.
Nearly two thousand years later (1510), Leonardo da Vinci stated
that fossils were the remains of former living animals.

The Lamarckian theory of evolution. Jean de Lamarck (1744-

371

372

PROGRESSIVE DEVELOPMENT

' Am. Museum of Nat. History

The skeleton of an amphibian dinosaur, the Brontosaurus, was unearthed in Wyoming in
1898. The animals shown above have been restored by placing muscles and skin over the
assembled skeletons. These animals probably ate soft plants and lived in shallow waters and
are thought to have crawled out upon land to lay eggs.

1829), a Frenchman, set forth his ideas on evolution in his book,
La Philosophie Zoologique. He coined the expression use and dis-
use to summarize his ideas of the causes of variation in species.
He thought that organisms could adapt themselves to fit the envi-
ronment. He supposed individuals acquired the characters they
needed and these acquired characters were transmitted to their
offspring. For example, he said that the original giraffe had a
short neck. For some reason, it began to eat leaves from trees and
was constantly stretching its neck to reach them. Consequently,
the neck started to grow longer and the offspring were born with
longer necks. According to Lamarck's theory, if a man developed
his mind very carefully, his children would start with better minds.
His theory has been generally discarded. Our present knowledge

THE DARWINIAN THEORY OF EVOLUTION

373

of heredity does not show that characters acquired in the life
time of an individual organism are inherited.

Recently, there has been a revival of interest on the part of cer-
tain modern scientists in Lamarck's theory. They base their ideas
on the supposition that over- or under-development of an organ
produces hormones in different amounts, which may affect a gene
in the germ plasm and cause variations.

The Darwinian theory of evolution. The theory of natural
selection was set forth in the book, Origin of Species, by Charles
Darwin (1809-1882), but it was also formulated independently
by Alfred Russel Wallace (1823-1913). Herbert Spencer (1820-
1903) has exerted a profound influence upon thinking people
through his philosophical writings on evolution. Darwin's theory
is based largely upon deductions made from observations that he

Am. Museum of Natural History
Restoration is shown of a prehistoric reptile, Allosaurus, one of the largest carnivorous ani-
mals that ever lived. It was forty-seven feet long with its head twenty feet above the ground
when it stood upright. Below is the skeleton shown as unearthed. From its position, scientists
think that it was feeding on one of the giant herbivorous dinosaurs just before its death.

374 PROGRESSIVE DEVELOPMENT

made after reading Malthus' Essay on Population and from mate-
rial gathered during his trip around the world on a ship commis-
sioned for, scientific exploration. It consists of the following
principles. (1) Overproduction. More individuals are produced
than can possibly reach maturity and reproduce themselves^ A
plant commonly called the shepherd's purse may produce upon a
single stalk as many as 64,000 seeds, and a tobacco plant may pro-
duce 360,000 seeds annually. A single fern plant produces about
fifty million spores a year. If all these spores matured; the United
States would be covered with ferns in two years. A single salmon
may lay 2,000,000 eggs, a female codfish 9,000,000 eggs, and a Vir-
ginia oyster not less than 15,000,000 eggs. The sea would be a
mass of writhing, struggling fish in three years if all survived. This
overproduction leads to (2) a struggle for existence. Whenever
there are abundant offspring, there must be ample food and room
for life and development. Crowding makes the existence of indi-
viduals a real contest or fight. A struggle ensues for obtaining
food, for finding a mate, and for producing more young. All can-
not survive. Those that do are better adapted to meet the
conditions of their environment than the rest. It is a well-known
fact that all the individuals of a species are not the same. Some
are swift and some skillful, which help them to survive. These
slight differences are known as (3) variations. These variations
play a most important part in the struggle for existence. Each
one that is swift of foot, strong, skillful, or protectively colored
possesses a variation that fits him to his environment better than
those that do not possess such a variation. Variations make
animals unequal in the contest of life. There is a struggle for
existence : some are killed off ; others, the fittest animals or
plants, survive. Thus overproduction intensifies the struggle for
existence ; this struggle results in (4) the survival of the fittest.
Darwin's theory of selective survival is often called " natural
selection." (5) Variations are usually inherited. Those slight

THE DARWINIAN THEORY OF EVOLUTION

375

variations which tend to fit a species into its environment are
passed on to the offspring and thus a new species will eventually

Am. Museum of Nat. History

The earliest horse, the Eohippus, had four toes and the splint of the fifth toe on the fore-
foot. The Mesohippus had three toes with a rudimentary fourth toe. In the Merychippus,
only one toe reached the ground in walking. In the Hipparion one toe became greatly de-
veloped and the other toes became more rudimentary. The Pleistocene horse, Equus, and
the recent horse show this same characteristic. There were corresponding changes in the
fore-feet, skulls and sizes of the various horses.

arise. Since these desirable variations are preserved by heredity,
each generation is better fitted to the environment than the pre-
ceding one. And so Darwin believed that through the passing

376 PROGRESSIVE DEVELOPMENT

r?£ "ft ^"C

Museum of Natural History
From fossil evidences, the evolution of the horse has been reconstructed. There

of years this slow accumulation of variations will lead to new
species as well as to a great diversity in one species.

There are a great many facts to support Darwin's theory of
natural selection, although some objections are made to it. (1)
Variations are frequently not inheritable, Darwin did not dis-
tinguish between somatic and germinal variations. (2) The varia-
tions frequently do not have anything to do with the fitness of the
organism for its environment. (3) The struggle for existence
does not necessarily weed out the unfit organisms. Frequently,
the weeding out occurs before the organisms have grown sufficiently
to have their characteristic differences appear. Plants and ani-
mals are frequently killed off by agencies, forces, and accidents
that do not discriminate between the fit and unfit.

The de Vries theory of evolution. The theory of mutation was
formulated by Hugo de Vries, a Dutch botanist, in 1904. He
published his ideas in a book called Species and Varieties. Charles
Darwin had collected many examples of organisms strikingly
different from the other members in the species. These he called
sports. He did not attach very much importance to them. Hugo
de Vries based his theory of evolution on sports which he called
mutants. Weismann's conclusions in regard to germ plasm had
disproved the inheritance of acquired characters. He had claimed
that modifications of the body or somatoplasm did not affect the
germ plasm and therefore could not be inherited. This fitted in
with the ideas of Hugo de Vries who had made direct observations

THE DE VRIES THEORY OF EVOLUTION 377

Museum of Natural History
has been a gradual increase in size from the most ancient to the present day horse.

on the appearance of mutations among the plants in his gardens
and greenhouses. He observed that mutants usually transmitted
their peculiarities to their offspring.

The theory of mutation differs from Darwin's theory of natural
selection, in the following facts. (1) Among individuals of a
species, different forms arise suddenly and independently, not
gradually. These forms differ widely from their parents. The
forms showing wide departures are mutations. In many cases these
mutations are inherited. (2) Mutations may take place in any
direction. They may or may not fit in with environment. They
may or may not be favorable. The main thing is that some are
capable of establishing themselves and some are not. (3) In gen-
eral, the unfit mutants are likely to be eliminated through natural
selection. (4) The fit mutants are likely to survive by natural
selection. The mutationist does not believe that natural selection
really starts the species. He believes that it controls the persist-
ence or disappearance of the mutant. The keynote to the theory
of mutations is that organisms must first appear with distinctive
qualities that are inheritable in order to start a new species.

There is practically no disagreement .among scientists concern-
ing evidences that organic evolution has taken place. But, there
is still much disagreement in determining which of the theories
thus far formulated most nearly fits the facts. The de Vries
theory of mutation is one that is generally accepted by many
scientists.

WH. FITZ. AD. BIO. — 25

378

PROGRESSIVE DEVELOPMENT

tip's

Part of a fossil backbone.

Am. Museum of Nat. History
Fossil footprints.

The age of the earth.
Before examining the
evidences of evolution
of present living
things, it is necessary
to understand some-
thing about Paleon-
tology, a science which
deals with the life of
past geological
periods. Geological time includes all the time since the earth first
started to be formed. Geologists have estimated the age of the
earth by the relative age of various layers of rocks and metals. For
example, the presence of a form of lead has been found in a Nor-
wegian mineral composed chiefly of uranium. Assuming that the
production of uranium ceased as soon as the earth and sun sepa-
rated, geologists have agreed that this lead is about three billion
years old. This was determined by estimating the length of time
necessary for a small amount
of metal uranium to break up
into this form of lead. From
this time and amount of metal,
the age of the lead and, there-
fore, the earth was calculated.
The cliffs in a valley will
show that rocks are laid in
strata or layers. The succes-
sive layers of the rock suggest
that they were deposited one
after another from the bottom
upward. The top stratum is

the mOSt recent One deposited. From drawing Museum Nat. Hist.

-o i • j* • l i i p i A colossal, hornless rhinoceros of prehistoric

.bach individual layer or rock days .

THE AGE OF THE EARTH

379

From drawing Museum Nat. Hist.
The shovel-tusked mastodon used
its scooplike jaw to gather up vege-
tation from the water.

constitutes a record of the time when
it was deposited. The thickness of
the stratified rocks now exposed upon
the earth surfaces of the continents is
very great. Knowing how slowly sedi-
ments accumulate upon the sea floor,
the age of the earth must measure ap-
proximately hundreds of millions of
years. Determining the arrangement
in which the strata were deposited is
difficult, because, in different areas,
different strata may be omitted for
one reason or another. Consequently,

the sequence is not always alike. In some areas a more recent rock
deposit is exposed than in others. Sometimes the rock deposit

may have been completely
weathered or worn away.
The formation of rocks differs
in various parts of the country.
Some rock was elevated from
the sea and forms the land of
to-day. This is known because
it contains fossils of shells of
animals that once lived in the
sea. The flatness of the beds
of rock seems to show that their
movement from the sea was so
uniform and gentle that their
Original formation could not
have been broken.

The oldest historical records
of Egypt or Babylon date back
perhaps six or seven thousand

From draining Museum Nat. Hist.
Fossils of Titanotheres, prehistoric mammals,
have been found in both Asia and America.
At the time they lived, Asia and America were
probably one continent joined where Behxing
Strait is now located.

ER/^S IPEBIODS

*y° ^^ig SfnTi

DawmANt XriFB

leisfcocgnejl

Cenozoic &j?««e

" Br "Eg ftamr

>IftMMALS
FLORA

S.ooo.ooo

Pateoroic

*18,ooo,ooo

$«*£mSn

■^iVuricth'i"--

"Or&ovieictn i

ii(|i (, ''pli^il|llllillliii(/|[(
wa«ibriarLi|(i
lllll^i i ii i iii' ft liii ^ l UlilHHl

HIGHER
5HEU£D

iTCesr^enaw&n

PftiMinve,

MARINE"

11,000 000

SvSbuHan*.*?

Archeozoic

■46,000,000 ^.

UNICELLULAR ^>.S-? V «V #

T te-e- ° V* » o* 1 <§ .'

IIFE^.

>ao
fo$$u«$

380

FOSSILS 381

years. Recently, an earlier Egyptian civilization has been
unearthed that dates back more than ten thousand years. The
carvings left by prehistoric man in the caves of the Pyrenees are
perhaps twice as old as the Egyptian culture just mentioned.
According to the evidence that is now available, man has prob-
ably existed only a few hundred thousand years. Beyond man
stretches a chain of varied forms which can be arranged in pro-
gression from the highly complex ones of to-day through simpler
and simpler ones back to the simplest of all the one-celled plants
and animals.

Fossils. In the strata of rock are found fossils in all degrees of
their original state of perfection, varying from trails, tracks, or
imprints to perfectly preserved shells, wood, bones, and complete
skeletons. As a rule, it is only the hard parts of the animals and
plants which have been preserved from decomposition. Some-
times the original organic substance is preserved, but more often
it has been replaced by mineral matter. This slow process of
replacement is known as petrification and the organism or the
part of the organism is said to be petrified. In a skeleton of a
prehistoric animal, particle by particle the lime was replaced by
indestructible silica, the element found in stone, sand, and glass.
Probably the most common forms of fossils are molds or casts.
The dead animal or plant fell into soft mud in which it made an
impression which was preserved long after the organic matter
had been destroyed. Sometimes these molds harden or became
filled with a substance which formed stone.

Evidences of evolution. The organized data that support the
development of the higher organisms from the lower ones are based
on the following evidences: (1) geological evidences, (2) geo-
graphical evidences, (3) morphological evidences, (4) vestigial
evidences, and (5) embryological evidences.

Geological evidences. The oldest known rocks appear to have
no fossils in them. The next layer shows traces of life of the

382 • PROGRESSIVE DEVELOPMENT

simplest character. The fossils of the most highly developed
animal, so far discovered, found in the oldest rock (Paleozoic)

Flying reptiles, the pterodactyls, were probably
the ancestors of our modern birds.

are those of an animal related to a crab, called the trilobite. As
higher layers of rock are reached, fossils of more complex animals
are found. These are different, but obviously related to the
forms in the strata below.

According to the present-day evidences, all life at an early period
was in the water. The history of the development of life has
been formulated from records made in rocks. It is thought that
the most primitive forms probably appeared in the warm shallow
waters of the flats between tides. First, there appeared plant
forms, algae; later, animal forms, protozoa. There was no life
on the land. The rocks and coarse soil were quite bare. Later,
countless minute creatures appeared in the water. Their shells
made up the great cliffs of chalk.

After centuries had passed an organism appeared that had an
organ for breathing air. It is thought that this form developed
from the more primitive types. The first traces of the land ver-
tebrates are the footprints of the amphibia. These are preserved
in mud molds which have solidified into rock.

GEOLOGICAL EVIDENCES

383

Some amphibia are thought to have developed into animals,
the reptiles, that breathed with lungs all their lives. The reptiles
of the past are called dinosaurs. Those of the earlier Mesozoic
period were small, but in the latter part of the period, they be-
came more numerous and gigantic in size. The Brontosaurus
was nearly seventy feet long. (See page 372.) The Allosaurus
was a trifle smaller. It was a dragon-like creature that preyed
on its larger but clumsier relatives.

During this period, the pterodactyl, a huge bat-like animal,
appeared. It glided through the air by means of folds of scaly
skin extending from the fore-limbs to the side of the body. It
had a large bill and a long tail. Its wing-spread was thirty feet.
This is probably the animal that was transitional between birds
and reptiles. The Archae-
opterix was another an-
cient birdlike form. It
has long, grill-like, true
feathers on its wings, a
small jaw with teeth, and
a vertebrated tail with
feathers attached. There
were claws on its wings.
No transitional animal has
been found showing how
the scales of the reptiles
developed into the feathers
of the birds.

While the birds were
developing, a small, very
inconspicuous group of
animals made their ap-
pearance. They had hair
instead of scales, and had

Am. Museum Nat. History

The Archaeopteryx is the earliest known bird.
Two fossil skeletons were found in Bavaria. The
creature was about the size of a crow, covered with
feathers as in modern birds. Unlike present-day
birds, it had uniform teeth in both jaws. It probably
used all four limbs in climbing trees. The clawed
digits were adapted for this. It is probably an in-
termediate form between reptiles and birds.

384

PROGRESSIVE DEVELOPMENT

a nourishing fluid for their young in certain glands of their skin.
Their rate of metabolism was much higher than the reptiles.

Am. Museum Nat. History

The Paleozoic period is noted for its luxuriance of plant growth. Ferns, club mosses, and
ferns related to the horsetails attained the size of trees and formed dense forests. Many
cone-bearing trees are found, but none of the higher types of flowering plants. As the plants
died and became part of the swamps, some unusual tremendous pressure transformed them
into coal beds.

Hence they are called warm-blooded. They retained the eggs
inside their bodies until the young were almost fully developed,
and supplied them with nourishment during development. These
were the mammals. The platypus or duckbill of Australia is
thought to be a transitional form between the egg-laying birds and
the mammals. It is furry, has a bill like a duck, lays eggs, and
feeds, its young with milk (page 513). The marsupials, such as
the kangaroo, are somewhat transitional. The young are born
before fully developed. They climb into a pouch in the abdo-
men of the mother and complete their development there. From
the early mammals of the Cenozoic era have developed the many
species which dominate the earth to-day. Man belongs in this
great group of mammals.

GEOGRAPHICAL EVIDENCE 385

Geographical evidence. It has been found that every group of
organisms expands its range just as far as conditions permit. Re-
gions in every way similar, so far as climate, soil, and other condi-
tions are concerned, are inhabited by totally different plants and
animals. Thus, the climate of Australia is not very different
from some of North America, but the animals and plants living
there naturally are not like those of North America. The same is
true about other- similar regions.

Regions that are very different are occupied by forms of plants
and animals that are sufficiently similar to be considered of the
same families. For example, goats and sheep, obviously related to
each other, are found in tropical, temperate, arctic, and antarctic
circles. They are thus living in varied surroundings.

Darwin pointed out that where similar regions are occupied by
different flora and fauna, these regions were always separated from
each other by impassable barriers such as oceans, mountain
ranges, and deserts. Thus Australia and America were always
separated by the ocean, and land animals could not migrate from
Australia to America. On the other hand, where similar plants
and animals inhabit regions that are markedly different in their
climate and soil, these regions are either connected directly, or
show evidence of having been connected in the past. For ex-
ample, the plants and animals found in oceanic islands are fre-
quently related to the inhabitants of the nearest mainland.
There is some evidence that tends to show that the islands Were
a part of the mainland at one time.

The Mongolian Expeditions. It has been known for some
time that Behring Strait formerly existed as a land bridge con-
necting America with Asia. It is thought that a similar connec-
tion, by way of Greenland, connected America with Europe. It
was observed that the animals of North America, Europe, and
Asia north of the Himalaya Mountains were somewhat similar
and it was thought that animals must have crossed these areas

386

PROGRESSIVE DEVELOPMENT

■s>rrist

liumerics

2. t^^^s vwSitcs

man

xvWst, .vclncs *>vcmerus

r*cr elites

cov

wist

humerus

raaius

horse

V/dst

and mingled. For example, American camels and horses "may
have migrated to Asia or vice versa.

It was also known by
geologists that the Gobi
Desert, Mongolia, in Asia
was elevated from the sea
during the period of time
when reptiles were abun-
dant. It became dry
land at that time and
has remained dry ever
since. The American Mu-
seum of Natural History
financed expeditions,
headed by Roy Chapman
Andrews (see frontis-
piece), to Mongolia to
investigate the desert for
remains of reptiles. Since
reptiles were the prede-
cessors of man, it was
hoped that a transitional
form between the reptiles
and man, or between the
early mammals and man,
would be unearthed.
Because of climatic con-
ditions, deserts are pecu-
liarly fitted to preserve fossils. Few people have penetrated and
lived in the desert, so fossils are more or less undisturbed. Asia
was thought to be a dispersal center to Europe on one side and
America on the other. These expeditions have met with the
greatest success in unearthing remains of reptiles and early

*\vha1e

wrj>fc

There seems to be a common plan of structure in the
limbs of various vertebrates which points to a common
ancestor.

MORPHOLOGICAL EVIDENCES

387

snake

mammals. Dinosaur eggs and dinosaur bones are there in abun-
dance. The largest mammal ever found has just been un-
earthed. Many of these fossils are on exhibition in the American
Museum of Natural History in New York.

Morphological evidences. There is great similarity in the
structure of animals, particularly the vertebrates. It is thought
that the bones which form the shoulder and hip girdle of man
are analogous to the bones which support the front and rear fins
of the fish. The bones of the arm and leg are variations of the
bones in the fin. Between y^^^^^-r — feimxr-,

the bones of the higher apes -"hm& limb

and man there seems to be a
difference in proportion only.
There is also a muscle for
muscle correspondence.

Vestigial evidence. There
are traces or rudiments of
organs found in certain
higher animals. These ves-
tiges are no longer used.
Probably the animal passed
through a stage when it used
such an organ. The horses
of to-day have splints or use-
less bones high upon either
side of their hoofs. These
are vestiges of toes. This is
one of the evidences that
the present one-toed horse
developed or evolved from
the ancient four-toed horse.
Human beings have a great many vestiges. The appendix is
large and performs an important digestive function in some ani-

wctitcctvng,

"Jpclvic Taones

" fior-poise

A striking evidence of descent is the rudimen-
tary organs in higher animals. The snake shows a
rudimentary pelvis and hind limbs. The nictitating
membrane is still found among birds and reptiles.
The porpoise shows vestigial pelvic bones. There
are numerous other rudimentary organs in various
animals.

388

PROGRESSIVE DEVELOPMENT

mals ; in man, it is a vestige. The muscles of the ears of human
beings are quite functionless although they are of value in aiding
lower animals to hear.

Embryological evidence. All animal embryos go through the

^sb salamander* -Tortoise Chick sheep

Vttfei'bifc "Viixmcxn.

Embryos of various animals appear to go through very similar stages. Before differentia-
tion has progressed very far, it would be very difficult to recognize a particular embryo. In the
later stages of embryonic development, species take on special characteristics.

blastula and gastrula stages. The most primitive many-celled
animals we know are the sponges. They are simple gastrulae.

The embryos of many vertebrates show similarities that are
not noticed in the fully developed organisms. They all go
through a similar early development. The nearer alike the adult
organisms are the longer they will show similarities in their de-
velopment. The higher vertebrates, the mammals, in their early
stage of development, have gill openings similar to those found in
fish. During embryological development, the diaphragm, which
in the fishes shuts off the gill chamber from the rest of the body,
in the human embryo moves well down into the body cavity.

While the human embryo is at one stage in its development, it
has a tail-like structure. The generalization of the development

EVOLUTION OF PLANTS 389

of embryos is known as the doctrine of recapitulation or the bio-
genetic law. It states that the organism, in the course of its
growth as an embryo, goes through stages similar to those through
which the whole race has developed. This theory was first ex-
pressed by Professor Haeckel, a German embryologist. Remember
three words — ontogeny recapitulates phylogeny. Ontogeny is
the history of an individual; recapitulates means repeats; phy-
logeny, the history of the entire race or group.

Evolution of plants. It is thought that plants, too, have gone
through an evolutionary series, but because they have little in the
way of skeletons to fossilize, less is known about their early his-
tory than about animals. Early vegetation consisted of luxurious
growths of mosses and ferns. One descendant of these primitive
fern groups is called the giant Equisetum or horsetail. It is com-
monly found growing along railroad embankments. This vegeta-
tion died, decayed, and collected to a depth many feet in thickness.
It became buried beneath newly deposited soil and was later
pressed and heated by volcanic action. Ancient forms of bog
mosses formed peat. Prehistoric ferns and allied plants formed the
basis of our present-day coal deposits. Some fossils of the forms
of vegetation then growing are preserved in the coal. The earlier
plant forms had certain primitive forms of fibrovascular bundles.
Many modern plants, though they have developed a more complex
form, grow the primitive form first. Later came the seed-bearing
plants.

. Questions and Suggestions

1. What is evolution ?

2. What are some of the ideas on evolution held by ancient scien-
tists?

3. Discuss the use and disuse theory of the origin of species.

4. Discuss the natural selection theory of the origin of species.

5. Discuss the mutation theory of the origin of species.

6. What practical difference does it make which theory of evolu-
tion proves to be true ?

390 PROGRESSIVE DEVELOPMENT

7. How would Lamarck, Darwin, and de Vries explain the fact
that horses in the north have longer hair than horses in the south ?

8. How would Lamarck, Darwin, and de Vries explain the fact
that the ancestors of giraffes had short necks and present-day giraffes
have long necks ?

9. Discuss the formation of the earth.

10. How have scientists been able to determine, even approxi-
mately, the age of the earth?

1 1 . What is one of the estimates given of the age of the earth ?

12. Discuss the formation of different types of fossils.

13. Name five lines of evidence given to support the theory of
organic evolution.

14. Discuss the relation of the age and formation of strata of rocks
to the fossils found in them.

15. In outline form give the sequence of fossils found in rocks be-
ginning with the fossils first found and going through those found in
youngest rocks. What relation does this sequence bear to the sim-
plicity and complexity of the animals ?

16. Name three different types of mammals and give the distin-
guishing characters of each type.

• 17. Discuss the geographical evidences of evolution.

18. What is the importance of the expeditions to the Mongolian
desert ?

19. Give examples of morphological evidences of evolution?

20. What are vestigial evidences of evolution? Give examples.

21. What are embryological evidences of evolution? Give ex-
amples. *

■ 22. Discuss the evolution of plants.

23. Discuss coal formation.

24. Give a report on the life and work of Lamarck, Charles Darwin,
and de Vries.

25. Look up and report on one of the Mongolian expeditions.

Supplementary Readings

Haupt, Arthur W., Fundamentals of Biology (McGraw-Hill Book Co.).

Holmes, S. J., General Biology (Harcourt, Brace & Co.).

Jewett, F. G., The Next Generation (Ginn & Co.).

Osborn, Henry Fairfield, From the Greeks to Darwin (Charles Scribner's Sons)

CHAPTER XXXVIII V

BACTERIA

Photomicrograph of spirilla. Photomicrograph of cocci.

What are parasitic bacteria f How can bacteria be studied? What
conditions favor the growth of bacteria? What is the relation of bac-
teria to food preservation ?

Bacteria possess no chlorophyll. They cannot make their own
food ; they are dependent upon other organisms for their nour-
ishment. They, with many other plants lacking chlorophyll, be-
long to a subdivision of Thallophyta. All bacteria are not harm-
ful. Life on earth would probably cease were it not for the
activities of certain bacteria. The disease-producing bacteria are
known as pathogenic types.

Structure of bacteria. When unstained, bacteria are colorless,
transparent cells with comparatively thick cell walls. The nu-
cleus is not organized, but nuclear material is scattered through
the cytoplasm. Sometimes the cell wall absorbs water, becomes
swollen, and forms a mucilaginous mass. The " mother of vine-
gar " represents a mass of cells of this type. Another example is
the mass of mucilaginous material that sometimes clogs the drain-
pipe of the ice box. In other types, the wall becomes gelatinous
and thick, and forms a capsule around the individual bacterium.
In certain bacteria, small granules are found, which are probably
reserve supplies of food. These particles absorb dyes readily and
hold the stain very effectively. Some bacteria have one or more
whiplike projections of protoplasm called flagella. They are the

391

392

BACTERIA

Rod-shaped bacteria, bacilli, sometimes occur singly. They may form strings and are then
known as streptobacilli. They sometimes have projections of protoplasm, somewhat similar
to cilia, called flagella.

<S> <S> CO
00 . OP 00 _

0D <P * CD

CO ^

Spherical bacteria, cocci, may occur in pairs, diplococci; or in chains, streptococci; or in clus-
ters, staphylococci.

%2y

^/w

The spiral bacteria, spirilla, may not have flagella, or they may have them. These bacteria
are always recognized by their twisted shape.

motile bacteria and are able to move through the water by means
of these structures.

There are many different species of bacteria. Most of them
may be grouped as one of three forms. These are the bacilli
or rod-shaped bacteria, the cocci or spherical, and the spirilla or
spiral. Bacteria vary greatly in size and shape within the same
group, although they are all microscopic. The micron is the unit
of measurement in microscopic work. It is about one-thousandth

PHYSIOLOGICAL FUNCTIONS OF BACTERIA

393

Photomicrograph of spirilla.

For example, the pus in the

of a millimeter in length or about one twenty-five thousandth

of an inch. Bacteria usually vary from 0.5 to 5 microns in length.
There is probably a very large

group of disease-producing agents,

which may or may not be bacteria,

that have never been seen with the

microscope. They can pass

through ordinary bacteria-proof

filters, and are known as filter

passers or a filterable virus. These

infectious microorganisms may be

found in the secretion, the excre-
tion, or blood of the body, and may

be passed directly from one person

to another, thus causing a disease.

abscesses on the skin of a smallpox patient is a filterable virus.

This material will generally produce smallpox if it is brought in

contact with a well person.
Bacteria are sometimes classified according to their relation to

oxygen. Those that need free oxygen in order to live, are the

aerobic bacteria, and those that live only in the absence of free
oxygen and perish if exposed to it are the
anaerobic bacteria. Certain forms of bac-
teria of decay thrive without air. They
obtain their oxygen by breaking down oxy-
gen-containing compounds.

Physiological functions of bacteria. No
bacteria are completely independent. They
lack chlorophyll and are, therefore, un-
able to make their own food, but have to
depend upon other organisms for it. Those

bacteria that inhabit and obtain their food from living organisms,

sometimes causing damage to those organisms, are the parasites.

WH. PITZ. ad. bio. — 26

Photomicrograph of strepto-
bacilli enveloped in a muci-
laginous sheath.

394 BACTERIA

They are not all necessarily harmful. Certain bacterial parasites
are found in the intestinal tracts of animals, but they do not
seem to produce any serious effects. The pathogenic bacteria
are all parasites. All of these are harmful.

Bacteria that inhabit and obtain their food from nonliving
organic material are saprophytes. The bacteria that decay dead
organisms are saprophytes. The bacteria that change alcohol
to vinegar, sour milk, and ripen cheese are saprophytes. Practi-
cally all of these are useful to man.

When a parasite and its host both flourish, and each one pro-
motes the growth of the other, their relation is one of mutual help-
fulness and is known as symbiosis. Each member, the bacterium
and its host, is known as a symbiont. For example, certain bac-
teria, known as nitrogen-fixing bacteria, live in little nodules or
swellings on the roots of clover plants. These bacteria take free
nitrogen from the air and build it into nitrates which the plant
can use. The clover plant uses some of these nitrates for making
protein. At the same time the bacteria absorb sugar from the
clover plant and use it for food. Neither organism suffers from
this relation and each one benefits from it.

Nutrition. All types of bacteria give off digestive juices or
enzymes which digest the food upon which they are living. This
food may be mineral nutrients, dead plant and animal tissue, or
even living tissue. Digestion is external to the cell, not within
the cell, as it is in the amoeba. For example, the tuberculosis
bacilli digest certain cells of the body, then absorb the digested
material. Practically all bacteria absorb protein from other
organisms. The absorbed protein is either assimilated into new
protoplasm or oxidized for the release of energy. As a result of
assimilation, the bacteria grow, divide, and form groups or colonies.

Reproduction. After the bacterium reaches its maximum size,
it builds a cell wall across the middle of the cell and thus divides
in half by fission. If conditions are favorable, certain bacteria

METHODS OF IDENTIFYING BACTERIA 395

may divide every twenty minutes. A single cell may produce mil-
lions of cells within twenty-four hours. As bacteria divide and
cling together, the mass of similar cells is
known as a. colony.

If conditions are unfavorable, many bac-
teria will give off moisture, thus lessening
their size, and surround themselves with a
thick wall. In this form, the cell remains
dormant until conditions are again favor-
able for development. This is known as a

r Different types of spores

spore. All bacteria cannot form spores. are f0 . und amon s bacteria.

Sometimes the spore forms

Spore-formation in bacteria is not a type at one end of the ceil and

. . * .. sometimes in the center.

oi reproduction because no new cells are

developed. It is a method by which the cell exists during un-
favorable conditions. Spores may be dried without injury. Some
spores may be heated to a high temperature, and the organism
will still remain uninjured.

Methods of identifying bacteria. Bacteria are so small that
other methods of identification must sometimes be used besides
their shape, size, and flagella. Some are recognized by their abil-
ity to hold an acid stain, or to give particular color reactions
with certain stains. Others are recognized by the changes they
bring about in or on various substances on which they are grown.
These substances are called media. The type of colony formed
is also a means of identification. Some produce colonies with
smooth, scalloped, or fringed edges. In some, the colonies are
opaque; in others, they glisten. Different colonies of bacteria
are characterized by different pigments. Some of the pigments
are gray, yellow, pink, or brown. Some colonies develop on the
surface of the media, others beneath the surface. The place and
character of the spore formed are other means of identification.
In some, the spore forms at one end of the cell ; in others, in the
middle. A tetanus bacillus forms a spore at one end of the cell.

396

BACTERIA

It swells out and the bacillus looks like a drumstick. The diph-
theria bacillus is characterized by granular particles which turn
red with a certain stain and will not lose this stain.

A method of identifying bacteria is through recognition of the types of colonies they form.
Some colonies are translucent, others are opaque ; some have regular margins, others have
irregular margins. One of the above plates has been exposed to bacteria, the other plate has
not been opened and is sterile. This is called the control.

Media for cultivation of bacteria. Beef broth is the principal
medium used for the cultivation of bacteria. If a small quantity of
the seaweed, agar, is added to this, a solid medium results. Some-
times gelatin is used in place of agar, and prune juice, sugar
solution, or blood instead of beef broth. The nutrient medium
which will furnish the best nourishment for the particular bac-
terium is selected.

Bacteria are usually grown in Petri dishes or on agar slants in
test tubes. The Petri dish was originally devised in 1887 by R. J.
Petri in a Berlin laboratory. It really consists of two dishes,
each one being a shallow glass saucer with a perpendicular rim.
One fits rather snugly as a dust-proof cover over the other.

First, the agar medium is boiled and filtered two or three times.
The Petri dishes are thoroughly cleaned and sterilized. The hot
sterile agar is then poured into the dishes. Great care is taken,
in order to prevent any bacteria in the air from entering during
the pouring or plating of the agar.

OCCURRENCE OF BACTERIA

397

In preparing agar slants, the test tubes must be plugged with
sterile cotton and sterilized thoroughly. Then, the plug is re-
moved, the sterile agar quickly poured in, and the plug put back
in the mouth of the test tube. The test tubes are usually set
obliquely for the agar to cool, so that, when firm, the surface of
the media is slanting. Hence the term agar slant. This method
gives more surface for the growth of bacteria.

In order to introduce bacteria for cultivation into a Petri dish,
the dish is uncovered and exposed to the air. After the expo-
sure, the dish is kept closed. Bacteria may also be introduced
with water, food, dust, or other foreign material. In introducing
bacteria into the agar slant, the cotton plug is removed carefully
so as not to get bacteria on it. The agar slant is then streaked
or stuck with a needle infected with bacteria.

Occurrence of bacteria. Bacteria are so extremely minute that
they float in the air with the particles of dust. It is almost im-
possible to find any air that does not contain them. Since this

r " >*»*,

One way of growing colonies of bacteria is on an agar
slant preparation. The surface of the agar is streaked with
the material containing the bacteria. The long slant gives
considerable surface on which growth may take place.

is the case, it is quite impossible for any material exposed to the
air, for even a short time, to escape contamination from bacteria.

398

BACTERIA

Practically all bodies of water on the surface of the earth contain
great numbers of bacteria. The numbers in different kinds of water

•slant smzcccs
B.coli tt.atththeriae

•Stab CuYtures

Two types of inoculations, smears and stabs, are made on slant cultures. After the media are
incubated, the germs grow into colonies, each having a characteristic form and shape.

vary according to the location of the water. In spring water, the
number of bacteria is relatively small, but in water into which sew-
age from cities drain, the number' is extremely large. Sometimes
bacteria in water contaminated with sewage are disease producing.
The soil that has been well cultivated is usually rich in bac-
teria. The deeper layers of soil contain few or no bacteria.
Where the soil is dry and sandy, there are relatively few bac-
teria; where it is moist and loamy, they are abundant. They
are found in great numbers around the bodies of dead animals or
in soil that contains decaying roots of plants.

GROWTH OF BACTERIA 399

Bacteria are probably found on all cooked foods which have,
been exposed to the air, as well as on the surfaces of all fruits
and vegetables.

The relation of various conditions to the growth of bacteria.
Most bacteria thrive best in darkness. Direct sunlight kills them
after a few hours of exposure. Even spore forms may be killed by
direct sunlight. The food of bacteria must be organic and must
be slightly moist. The best temperature for bacterial growth on
culture media is between 20°^ and 40° C, although bacterial life
is possible at absolute temperature (— 273° C.) and at 160° C.
The temperature varies with the particular type of organism. For
example, the human tuberculosis bacillus grows best at blood
heat, 37.5° C. ; the bird tuberculosis bacillus grows best at about
42° C. Sudden changes in temperature are more or less detrimen-
tal to bacteria. If changes are slow, the spore formers will have a
chance to form their spores. Cold checks the growth of bacteria
and continued freezing or alternate freezing and thawing may
sometimes kill them. Different bacteria are killed at different
temperatures. Active typhoid bacteria are killed when subjected
to a temperature of 60° C. for thirty minutes. Ordinarily, all
bacteria are killed at 100° C. Moist heat is found more effective
for killing bacteria than dry heat.

Methods of food preservation. Substances may be freed from
bacteria, or the action of the bacteria on the substance may be
materially decreased by depriving the organisms of some condi-
tion that is necessary for their life or growth. Some of the
methods of preserving foods against the action of bacteria are
dehydration, refrigeration, canning, smoking, and addition of
preservatives.

If a food is thoroughly dried, particularly by the sun, the bac-
teria cannot thrive. The sun, in all probability, will kill them.
Dryness is also an unfavorable condition for the growth of bac-
teria. Refrigeration preserves foods because cold checks the

400

BACTERIA

A method of preserving foods is by sun-drying The picture shows plums exposed to sunlight
until dry. This changes them to prunes and safeguards them from the attacks of bacteria.

growth of most bacteria. In the refrigeration process, the flavor
is not likely to be spoiled. It is an expensive method, however.
Canning or preserving makes use of extreme heat to sterilize, then
by placing the food in air-tight containers no new bacteria can
enter. Smoke contains creosote, which is poisonous to bacteria,
but, in small amounts, is not poisonous to people. Hence, smok-
ing is a method of preserving food. Bacteria in an alkaline or
acid solution are more easily killed than those in a neutral solu-
tion. Housekeepers have found that canned fruits seldom spoil,
but canned vegetables frequently cause trouble. Sometimes
sugar, salt, and vinegar in quantity act as poisons to bacteria.
They are not injurious to people. Producers frequently add pre-
servatives such as benzoate of soda or mild acids to help kill the
bacteria. Many of. these may be injurious.

Problem. What is the number of bacteria found in the air in 'cari-
ous places in the environment ?

Prepare seven or eight Petri dishes of sterile agar media.

METHODS OF FOOD PRESERVATION 401

I. Keep one Petri dish closed throughout the experiment. This is the con-
trol and will serve as a comparison with the exposed dishes.

II. Expose one dish of the agar media in a classroom at head leveU ex-
pose one in the hallway through which many pupils pass ; one in the lunch
room, one in the gymnasium, one in the street, and one in a theater. Cover
all dishes immediately after exposure.

A. Incubate the dishes between 30° to 40° C. until colonies appear on
the surfaces.

B. Compare the dishes with the control.

C. Which dishes show the greater number of colonies ?

D. Which dishes show the greater number of different kinds of colonies ?

E. What seems to be the relation between dust and bacteria ?

Problem. What is the bacterial content of different kinds of milk f *

I Put a couple of drops of certified milk in a Petri dish containing
sterile agar. Cover the dish immediately and permit the milk to completely
cover the agar.

II. Repeat the experiment for grade A and grade B milk.

III. Incubate the dishes for twenty-four hours at between 30° and 40° C-

IV. Which milk shows the greater number of colonies ?

V. Which milk shows the greater number of kinds of colonies ?

VI. What is the danger of having a great number of kinds of colonies ?

VII. In selecting milk, state anything else, besides bacterial content, that
must be considered.

VIII. State one possible reason for using pasteurized milk and one reason

for using certified milk.

i
Problem. What is the effect of various antiseptics on the growth of

bacteria f

Expose each of five dishes of sterile agar media to dusty air in order to
inoculate them or introduce germs into them.

I. Cover one and keep it closed throughout the experiment.

II. Pour a little boric acid into dish number 2. Cover it and tip the dish
repeatedly until the boric acid completely covers the surface of the agar. Be
sure not to use any more than just enough to cover the agar.

III. Repeat the experiment, using iodine, salt solution, and mercurochrome
in each of the other three dishes.

* All cities do not grade milk as A, B, and certified. If different forms of grading
milk are used in your community, use those in performing this experiment.

40^ BACTERIA

IV. Incubate the six dishes for twenty-four hours.

V. Make repeated daily observations.

A. Which material used seems to be of least use in checking the
growth of bacteria ?

1. Compare the growth of colonies in this dish with your control.

B. Give the effects of each of the other solutions on the growth of
bacteria.

C. Which antiseptics might be unwise to use on delicate lining mem-
branes such as those in the throat, nose, and eye?

VI. The experiment may be repeated to test the results of various mouth
washes.

VII. Antiseptics should be used with great discretion. Some of them kill
bacteria rather than check their growth. They are called germicides. Those
that check the growth of bacteria are the true antiseptics. Germicides may kill
the tissues as well as the bacteria. This, in many cases, will check healing.

Questions and Suggestions

1. Describe the structure of bacteria.

2. Classify bacteria according to their shape. Give some in-
dividual variations of each type.

3. What are aerobic and anaerobic bacteria?

4. Discuss three different types of nutrition found among bacteria.
Give an example of each type.

5. Discuss reproduction and spore-formation.

6. Name five methods used in the identification of bacteria.

7. What is the importance of agar ?

8. Discuss the sterilization of agar and of Petri dishes. Discuss the
methods of inoculation, and conditions for the cultivation of bacteria

9. Discuss favorable conditions for the growth of bacteria. Which
of these conditions are found in the human body ?

10. Under what conditions will food spoil ?

11. Name some conditions unfavorable for the growth of bacteria.

12. Give in the form of an outline the method of preserving certain
foods from the activities of bacteria, and the resulting conditions that
are unfavorable for their growth.

13. Discuss the relative number of bacteria in different types of air.

14. Discuss the bacterial content of different types of milk.

15. What is the relation of different antiseptics to the growth of
bacteria ?

-mill*

lotftoVacilW?

V lactik J
* eccidL f

CHAPTER XXXIX

BENEFICIAL

ACTIVITIES OF

BACTERIA

or*

moth er of vfoiegor

aci<2t

« ©i>

vinegar

Curdling of milk.

Souring of fruit juices.

Why does milk turn sourf What makes sweet cider turn into
vinegar t Why will the dead body of an animal putrefy f What is
the importance of the rotation of crops f

Bacteria which are of value to man may be grouped into
three classes : (1) those necessary for the preparation of certain
foods; (2) those aiding industries; and (3) those useful in
agriculture.

Bacteria in food preparation. Certain bacteria in milk change
the milk sugar, lactose, to lactic acid. The production of this
acid coagulates or curdles the protein in milk. This process of
acid-formation and protein-coagulation is called souring. When
the acid reaches a certain concentration, the process ceases. The
presence of lactic acid in cream increases the yield of butter and
improves the flavor. Lactic-acid bacteria are necessary for the
production of sour-milk cheeses such as Swiss, Edam, and Ca-
membert. The flavor of these cheeses is partly due to the lactic-
acid fermentation and partly to mold activity.

Acetic-acid bacteria convert alcohol into vinegar. Yeasts first
attack the sugar of fruits or grains and convert it into alcohol, then
the acetic-acid bacteria attack the alcohol and change it to
vinegar. This vinegar is useful in preserving foods because
bacteria of decay cannot work in a ^strong acid medium.

403

404 BENEFICIAL ACTIVITIES OF BACTERIA

If cabbage is finely chopped, salted, and packed tightly in
jars or barrels, it will undergo a chemical change. The salt will

foool fooa.

Toticctei^ium.

■t=i

pathogenic
bacte-r

actei^itcTTL

acicl coocste toxin

When bacteria absorb and use food, they give off acid wastes. The wastes of disease-
producing bacteria are called toxins.

extract from the cabbage the juice which is a good medium for
the growth of lactic-acid bacteria. This will attack the tissues of
the cabbage, changing it to sauerkraut. Meat is made tender
by the action of bacteria. When meat is fresh, that is, soon
after the animal is killed, it is tough and more or less tasteless.
Bacteria attack the muscles and connective tissue, loosen the
fibers, and give the meat a taste. Meat is usually kept for some
time to permit this bacterial attack. This is the beginning of the
decay process. The process must not go too far or products that
are objectionable are formed, and the meat is said to be tainted.

Ensilage is prepared for stock by packing finely chopped fodder
in a silo. Bacteria and enzymes will attack the tissues of the
fodder, causing it to change in appearance, flavor, and nutritive
value.

Bacteria in other industries. Sponges are animals. The fairly
hard commercial sponge is really the skeleton of the animal. This
skeleton is composed of substances secreted by the cells of the
animal. The sponges of commerce are prepared by cutting their
attachment to the sea floor. The sponges are spread out on the
seashore and bacteria destroy the soft organic parts, leaving the
fibrous, horny framework or skeleton. This process is known as
curing. The exoskeletons are then thoroughly washed and
cleaned and sold for commercial uses.

BACTERIA IN INDUSTRIES

405

There are many different
bacteria which grow in milk.
A group attacks milk sugar
and produces lactic acid,

A similar process takes place in preparing linen fibers. Linen

comes from the flax plant. If the flax is cut and thrown into pits

and kept damp, certain bacteria will decay

the cementing materials which hold the

tough, strong fibers together. These fibers,

when separated, are used for the manufac-
ture of linen. This process of obtaining the

fibers of flax is known as retting or rotting.

There is an artificial process of retting which

is not as successful as the natural water

process. The natural process is used in

Ireland and produces a fine grade of linen. which results m - souring.

The artificial process, used in the United States, consists of an

acid treatment for loosening the fibers. It is much quicker than

the natural method, but less perfect, since the acid may roughen

the flax fibers.

Bacteria are valuable in curing tobacco. The tobacco stalks

with the leaves are piled into great heaps or hung from racks and

allowed to sweat and then ferment at a fairly low temperature.

This gives to tobacco its special flavor.

In tanning leather, the hides are soaked, scraped, and limed or

treated with acids to remove the hairs. The lime is removed,
and the hides are put into solutions of tan-
bark. During these processes, certain bac-
terial fermentations take place, which make
'the leather soft and pliable.

Bacteria in agriculture. Large quantities
of the nitrates from the soil are built into
proteins and protoplasm by the plants,
in fruit juices bacteria When these plants are removed, they take

change alcohol to acetic c "

a«d. with them the nitrogen in the form of

protein and protoplasm. The nitrogen of the soil would be
exhausted in a comparatively short time if there were no ways

406 BENEFICIAL ACTIVITIES OF BACTERIA

of replacing or renewing it. The same is true of sulphur and
potassium.

Bacteria of decay are essential in farming. They bring about
the decomposition of complex organic compounds into simpler
ones. When this is accompanied by offensive odors, the process
is known as putrefaction. The complex proteins and protoplasm
of the plant or animal contain nitrogen. When a plant or animal
dies, the bacteria of decay attack these nitrogen-containing com-
pounds and break them down into simpler substances. One of
these is a nitrogenous material, ammonia ; another substance con-
tains sulphur. Phosphorus and the other elements present may
be liberated, similarly. The decay process also sets free carbon
dioxide and water. Nitrogenous wastes of animals are usually
changed into ammonia by the action of the bacteria of decay.

Nitrification. Certain bacteria called the nitrifying bacteria
take the ammonia formed by the bacteria of decay and change it
into nitrates which the plants can utilize for further protein-
making. This process is called nitrification. Ammonia is a gas,
and would escape into the atmosphere were it not for the nitrify-
ing bacteria. Nitrite bacteria first convert ammonia into nitrites,
compounds formed by the union of ammonia with oxygen. Then
other organisms cause the nitrites to take up more oxygen and
form nitrates which are stable compounds and can dissolve in
the soil water. Nitrite and nitrate bacteria are always found
together. They work best in alkaline soils. If a sample of soil
is heated and thus sterilized, the action does not take place.
This indicates clearly that the process is a bacterial one and not
simply a chemical one. Nitrification takes place only in soil
that is well aerated and well drained. The drainage carries off the
acids that might interfere with the process. Aeration is necessary
because there must be enough oxygen to combine with the ammonia
to form the nitrites and the nitrates. Earth worms aid in this
process by constantly working through the soil. This permits the

DENITRIPIGATION

407

The soil bacteria are irreg-
ular-shaped organisms.

entrance of air. Lime is sometimes added

to soil to neutralize its acidity so that the

nitrifying activities may be increased.

Denitrification. If soil is poorly drained,

poorly aerated, and contains fresh organic

matter, denitrifying bacteria thrive. They

convert the ammonia, formed in the decay

process, into free nitrogen. The free nitrogen

then escapes into the air and is lost to the

plants. The denitrifying bacteria can also break down nitrates into

nitrites, then into ammo-
nia, and finally into free
nitrogen. Soil should
not be covered thickly
with unrotted manure as
the activity of these bac-
teria are then promoted.
From the point of view of
conserving soil fertility,
the denitrifying bacteria
are undesirable. Certain
other bacteria are able,
however, to take free
nitrogen from the air
and again change it into
a form in which it can be
used. These are called
the nitrogen-fixing bac-
teria.

Nitrogen-fixation. The
nitrogen-fixing bacteria

Nitrogen-fixing bacteria form nodules or small swellings , , , , ,.

on the roots of pod-bearing plants. The Countless bac- have already been (lis-
teria in these nodules fix free nitrogen of the air into a i • x l

usable form, nitrates. CUSSed in the preVlOUS

408

BENEFICIAL ACTIVITIES OF BACTERIA

chapter. When a pod-bearing plant, such as the clover, alfalfa,
bean, or pea, is young, its roots are attacked by the nitrogen-fixing

bacteria found in the soil. They
penetrate the roots through the deli-
cate roothairs and establish them-
selves in the outer layer of the root
cells. The root accommodates them
by building more cells in that region,
forming little nodules or tubercles.
In these nodules, the nitrogen-fixing
bacteria multiply. They take the
free nitrogen from the air which
permeates the soil, and build it into
nitrites which are later converted
to nitrates. When the roots of these
plants are plowed under, they decay,
and the nitrates are liberated into
the soil. Soil may be inoculated with
cultures of nodule bacteria. A crop
of clover or alfalfa plowed under
supplies the soil with about 100
pounds of nitrogen to the acre. Such
a crop is as valuable as many loads
of manure. A good crop of corn or
wheat will take from 50 to 75
pounds of nitrogen per acre from soil. There are certain free-
living soil bacteria which build nitrogen into nitrates when con-
ditions are favorable. The result of the activity of these organ-
isms is not unlike the nitrates formed by nitrogen-fixing bacteria.
But they differ from the nitrogen-fixing bacteria in that they do
not need roots of plants for their homes.

Lightning and similar electric discharges in the air unite some free
nitrogen with oxygen to form nitrates. These are washed from the

The value of nitrogen-fixing bacteria
was demonstrated in the above experi-
ment. When the roots of the plants
were examined, those on the left had
numerous well-developed tubercles ;
those on the right had no tubercles.
They were both watered with a nutrient
solution containing all the necessary
nutrients but nitrogen. Explain the
relation of the tubercles to the growth
of the plant.

ROTATION OF CROPS

409

air by rain and thus reach the soil. Exceedingly small quantities
of nitrates are formed in nature in this way. Commercial processes
of building nitrogen into
nitrates is now being con-
ducted in several sections
of the country. Com-
mercial nitrates are
generally used for ferti-
lizers. One of these
plants is at Muscle
Shoals, Alabama. The
excellent water-power
facilities of that location
supply the necessary
energy for the project.

Rotation of crops.
Crops are rotated, that
is, one crop succeeds a
different kind in the

same field year after year. The reasons for crop rotation are as
follows : (1) Plants use up varying amounts of the different min-
eral matters in the soil. One crop might need a quantity of
calcium salts but not much iron. Another crop will require
considerable iron but fewer sulphates. If one crop is planted year
after year in the same plot of land, that land will grow poor in one
or more mineral salts and the quality of the crops will be greatly
impaired unless commercial fertilizers are used. Where rotation
of crops is practiced, the same soil can be used for years without
adding fertilizer. (2) Plants are subject to diseases caused by
bacteria and other fungi. If only one crop is planted, the soil
may become infected with spores of disease-producing organ-
isms. Another crop probably would not be affected by these
spores. For example, corn smut will not injure potatoes; po-

WH. FITZ. AD. BIO. — 27

There is a continual building and destruction of carbon
compounds. This is described diagrammatically in the
carbon cycle.

410

BENEFICIAL ACTIVITIES OF BACTERIA

tato blight will not affect wheat. Rotation of crops also kills
insect pests that live only on a certain plant. (3) The un-
gathered roots and stalks of crops remain in the ground,
decay, and produce organic acids. These acids are sometimes
injurious to the plant producing them, but not to other plants.
Hence, the crops should be changed. Bone meal or lime is added
to neutralize these acids. Each commercial fertilizer used, how-
ever, adds that much to the farmer's expense. (4) Almost all
crops remove great quantities of nitrates from the soil. These may

SacteHoc

A number of different bacteria aid in transforming nitrogen into a form which plants can
use. There is a constant renewal of nitrogen in the soil.

be restored in a variety of ways. Animal waste, manure, may be
spread over soil and allowed to decay. This increases the nitrogen

SOIL CONSERVATION 411

content. Any organic material which decays will accomplish the
same thing. Many commercial fertilizers are made from guano,

cccrbohyclrates^^- ^ carboiv clio*i3e.> > ^ "*\^^" 03tf y^ en -

proteins_ v / \" Ur, f_T. / ^^-nilrat^S

-Salts \, /

There is an interdependence between green plants and animals. Animals can make use of
the oxygen excreted by green plants. These in turn, can make use of carbon dioxide, water,
and possibly urea excreted by animals.

bird waste. Refuse from abattoirs, and meat and fish canneries,
or specially prepared mixtures of chemical compounds, may be
purchased and plowed into the soil. The land may be allowed
to lie fallow, that is, unused for a season or so. Certain minerals
in the ground may break down in fallow fields and thus restore
the usable mineral elements. A leguminous crop, such as peas,
beans, or alfalfa, may be planted, allowed to grow, and marketed.
At the same time, nitrates are restored to the soil in which' they grow.
Soil conservation. If the soil is kept in good condition, nitrates,
sulphates, and phosphates are constantly renewed as they are
removed. The passage, use, and return of these materials consti-
tute a cycle as shown in the diagram. Were it not for the action
of bacteria in the soil, all vegetation on the earth would cease.
Soil fertility is primarily a bacterial activity. Bacteria are com-
monly thought of as being particularly injurious. In reality, the
beneficial effects of bacteria far outweigh the injurious effects in
many ways.

Questions and Suggestions

1. Using the following topics, make out a tabular outline of the
relation of bacteria to food preparation.

A. Name of bacterium.

B. Material attacked.

412 BENEFICIAL" ACTIVITIES OF BACTERIA

C. Material produced.

D. Commercial use of material produced.

2. Make a library report on the tanning of leather.
• 3. What is meant by soil exhaustion and soil renewal?

4. What is the importance of the decay process to agriculture ?

5. Explain nitrification in detail.

6. Discuss denitrification.

7. Discuss nitrogen-fixation. Give three different ways of fixing
nitrogen.

8. What is the importance of rotating crops ? Give at least four
reasons for rotating crops.

9. Mention four different facts that must be considered in culti-
vating soil.

10. Make out an original carbon and nitrogen cycle.

11. Do farmers have scientific knowledge about bacteria or do they
depend upon their experience or on hearsay in caring for the soil ?

12. Does the government make any effort to give farmers scientific
instruction in soil and crop improvement ?

13. Discuss a balanced aquarium.

Supplementary Readings

Gager, C. S., General Botany (P. Blakiston's Son & Co.).
Greaves, J. E. & E. O., Elementary Bacteriology (W. B. Saunders Co.).
Holman, R. M., & Robbins, W. W. A Textbook of General Botany (John
Wiley & Sons, Inc.).

^^- ' |

& Er

jj¥ra^ ■Kjt^tfi

k£

^^Jmij

^2^5w*?J

CHAPTER XL
HEALTH

\" w """1^8

Ewing Galloway
Push ball.

Ewing Galloway
Outdoor swimming pool.

Should people learn about diseases? Is longevity more or less con-
trollable? Has community or individual control of disease been more
successful?

Some people object to studying disease because they worry about
each disease studied, fearing that they have it or may contract it.
Education in health and disease should enable people to exercise
an intelligent attitude toward disease, to practice ways of prevent-
ing disease, and to learn how to conquer and control disease.

Disease and health. The best way of preventing disease is to
stay in good health. Some people feel that they are in a healthy
condition if no disease is present. Even though there is no actual
impairment of bodily functions, certain organs may not be in nor-
mal condition, consequently, health is not necessarily a lack of dis-
ease. Nor is the feeling of being well an infallible measure of the
degree of health. Frequently people feel very ill when the actual
illness is slight; on the other hand, people may have only a slight
feeling of discomfort and yet have a serious organic disorder. An
adequate measure of health is an annual physical examination.
If people are examined thoroughly every year, beginning symptoms
may often be detected before a disease has advanced to a serious
degree. Health examinations are just as important for well as for
sick people. In disease-control, prevention is far more important

413

414

HEALTH

Am. Museum Nat. Hist.

Bacteriological laboratories contain elaborate equipment. Can you identify the microscope,

Petri dishes, agar slants in test tubes, staining fluids for bacteria, distilled water in flask

for washing off excess stain, and the Bunsen burner ? Can you give the use of each article in

working with bacteria ?

than attempts to cure disease. Each illness, no matter how slight,
is likely to lower the resistance of the person just that much.

Health and longevity. Another misconception of health is that
it is identified by length of life or longevity. This; too, is
probably a fallacy. Some delicate people receive medical treat-
ment all their lives, and, through care, live a long time, although
they never really have good health. On the other hand, people
in perfect condition may meet with accidents which will cut short
the span of their lives.

Health and adaptability. Positively speaking, health is merely
the adaptability of the organism to meet a variety of situations. To
be healthy, an organism must be able to make rapid and proper
adjustment to every situation. For example, normal heart muscles
thicken to accommodate the heart to unusual conditions. A dis-
eased heart will not do this, consequently, discomfort results. Ac-
quiring resistance to certain diseases is a process of adaptation. All

HEALTH AND EDUCATION

415

people do not have an equal resistance. Those who have not
must learn how to acquire it. Therefore, education along
these lines is necessary. People must be taught hygienic living
so that they may adapt themselves properly to changes of tem-
perature, work, and food. Many diseases may be avoided by
correcting improper habits of living and certain physical defects.
Health and education. Health is one of the main objectives of
education. Unless the body can adequately adapt itself to chang-
ing conditions in life, the person is inefficient. In the past, undue
emphasis has probably been placed on defects. Open-air classes
were established for cardiac, anaemic, and tubercular children.
Nutrition classes were established for malnutrition cases. Each
year the health of some children was built up in these classes to
such an extent that the children were able to continue in regular
classes. Each year new cases would appear in regular classes which
would have to be sent to these special classes. Nutrition classes are

Underwood and Underwood
Play in the sunlight is the heritage of childhood. It leads to a proper physical development
and builds a healthy nervous system.

416

HEALTH

necessary, but if the entire school were properly educated in
health habits, and if there were a check to see that these habits,

A properly cared for set of teeth is the result of frequent expert inspection. In certain schools,
oral hygienists make surveys of mouths and suggest dental treatment when necessary.

once taught, were enforced in the home and community, there
would not be so many anaemic, cardiac, and tubercular cases.
In order to show how much education could accomplish in disease,
the Metropolitan Life Insurance Company and the National Tu-
berculosis Association conducted an experiment at Framingham,
Massachusetts. A campaign of education was carried on so suc-
cessfully that tuberculosis was reduced 69 per cent in that com-
munity within ten years.

Effective education in health is evidently needed. This is par-
ticularly pertinent when we consider that the statistics, prepared
by General Crowder of the United States Army, showed that
33 per cent of the United States soldiers in the World War were

SCIENCE AND HEALTH

417

unfit for front-line duty. They had been out of school a very
short time, but, evidently, had received very little, if any, instruc-
tion in health.

Science and health. In the Report on National Vitality, issued
by President Roosevelt's Conservation Commission on National
Vitality, it was claimed that the reasonable application of scientific
knowledge would add at least fifteen years to the average lifetime.
It stated that at least 40 per cent of American mortality was pre-
ventable or postponable. There are probably always three mil-
lion people ill in this country at one time. About 50 per cent
of this illness is probably preventable. This report was issued
in 1909. The expectation of life has gone up since that time from,
approximately, forty-five years to fifty-five years, according to the
figures of the Life Extension Institute.

Underwood & Underwood
Health is more often a matter of prevention than cure. In baby clinics, nurses weigh, measure,
and make various examinations of babies to make sure that they are in good health.

Along with the diseases that have been partially or entirely con-
trolled through scientific investigation and health education, there
has been a big drop in mortality. The deaths from typhoid fever

418

HEALTH

have been reduced 75 per cent, and typhoid is generally termed a
vanishing disease. The death rate of tuberculosis has been reduced

about 50 per cent. Diph-
theria is now preventable
and is becoming infre-
quent. In states where
prophylactic measures
are used, the Board of
Health expects to have
the disease under com-
plete control by 1930.
The diseases that may
be considered as largely
under individual control
show increasing death
rates. Heart conditions,
diabetes; and kidney
diseases are examples of
these. They are, to
some extent, dependent upon a person's habits of living.

It is an accepted fact that the general life expectancy span
at birth is increased. Believing that every one has the right to
live, science has enabled us to bolster up the weakling at birth
and all along the way — but eventually he drops out, the fight is
too great. Science has decreased the infant mortality rate only
to have the weaker ones die at a younger age than those with a
stronger physical start. If life is to be lengthened at the other
end, every individual must take more interest in, and insist on
living hygienically. Much is still to be done. Ten years could
be added to the expectation of life if all sections of the popu-
lation could live under the same favorable conditions that are
enjoyed by groups and communities where the death rates are
unusually low. Individuals must be educated to have an intelli-

Underwood & Underwood
A physical examination includes the taking of one's pulse
rate and temperature.

QUESTIONS 419

gent knowledge of disease and understand its prevention. There
are still too many defects such as mouth infection, tonsil infec-
tion, overweight, underweight, foot defects, and visual defects.
If all people had an annual health examination, many diseases
would be prevented. Disease prevention should be an incentive
for all people since it will reflect in the substantial gains in the
vitality of the nation. In the previous chapters, suggestions
concerning diets, sunlight, exercise, rest, and mental relaxation
have been given. In subsequent chapters methods of avoiding
actual diseases will be discussed.

The measurement of health. A test to show whether one's
personal habits are hygienic is the Payne " Habits and Practices
in Accident Prevention and Health " given in the Appendix. A
high school student should score at least 355 under A, 75 in the
items under B, and 70 in the items under C. The points total 500.

Questions and Suggestions

1. What is a popular objection to the study of disease ?

2. Name three popular misconceptions of health. Discuss the
fallacy in each of them.

3. Give a scientific definition of health.

4. How may health be attained ?

5. What can be accomplished by education in health ?

6. Why do we find a larger reduction in the diseases that a com-
munity can control, than in those that an individual must control ?
Why is this true ?

7. Discuss your ideas on an annual health examination.

8. Give some examples of adaptations of the organism to changing
conditions.

9. Discuss your ideas on the scoring of health practices.

" 10. Score your habits and practices, as suggested in the test in the
Appendix, on a separate piece of paper. Add the score and see how
closely you approximate hygienic living.

CHAPTER XLI

SMALLPOX AND
ITS CONTROL

Edward Jenner.

Keystone View Co.
Tribute to Jenner and
vaccination.

Has smallpox ever been epidemic? Is inoculation for smallpox a
new method of treatment f How did vaccination first start? What
effect has vaccination had on the mortality from smallpox?

History of smallpox. Smallpox was known in China many cen-
turies before the Christian era. It also existed in India, Arabia,
Ethiopia, and neighboring countries. It spread through Europe
during the Crusades. The first epidemic of smallpox in Europe
took place in the latter part of the sixteenth century. For centu-
ries, it was estimated that ten out of every hundred deaths were due
to smallpox. More than half the people in Europe were scarred and
disfigured by the disease. It is probable that at least 60^000,000
people died from smallpox during the eighteenth century.

The disease was first brought into America by the Spaniards
about 1515. Within a short period, three and a half million people
in Mexico died of it. Probably half of the American Indians died
during various epidemics of smallpox. Boston has had six epi-
demics ; in the last one, 1752, there were 5989 smallpox victims
out of a population of over 15,000 ; of these, 894 died.

History of inoculation against smallpox. Inoculation first origi-
nated in the Orient, hundreds of years ago. The people would
introduce into a cut or scratch of a well person, the pus or scab

420

HISTORY OF INOCULATION 421

from smallpox patients. This, in many cases, brought about
protection against the disease. The practice of inoculation was
carried into Europe by way of Asia, Africa, and Constantinople.
In Turkey, certain old women took pus from the pustules of per-
sons suffering from smallpox and inoculated it into the veins, of
well people.

In 1717, Lady Mary Montague, while traveling in Turkey, had
her little son inoculated with smallpox, and he did not contract
the disease. Through this incident, the idea of inoculation as a
preventative was introduced into England, although many people
were afraid of its results. Several years later, authorities offered
a number of criminals confined in the Newgate Prison, England,
their freedom, if they would submit to an inoculation against
smallpox. They did so, the results were satisfactory, and they
received their freedom. After this, the practice gained steadily
in England. When a person was to be inoculated, he was usu-
ally kept on a light diet for about six weeks. He was then
purged and bled to make sure that his body was in good condi-
tion. Then he was inoculated with smallpox. Pus was taken
from the pustules of a person with a mild case of smallpox and
placed in several scratches made on the body of the patient.
This usually resulted in a mild form of smallpox to the person
treated, but was supposed to protect him against a very severe
form. This method of inoculation was somewhat dangerous
to a community, in as much as new cases of smallpox, however
mild, were likely to develop.

History of vaccination. It had been a belief, for an unknown
length of time, in rural districts, that people who had contracted
cowpox, a disease of cows, did not take smallpox. A farmer
named Benjamin Jesty, in 1774, took some pus from the sore of a
cow with cowpox and inoculated his wife and children. This
made them immune to smallpox infection. But Jesty's experi-
ment never became generally known. It was Edward Jenner

422

SMALLPOX AND ITS CONTROL

(1749-1823) of England, who first made known the idea of vac-
cination. The germ theory of disease had not yet been pre-

^Prccssict

'^ST «■* J-«-r-r-O»00eD <© « COCO
jCftw <p CD COOOOXO <Sc0 <& CO COCO
S~£ ? :

A^strioc

|0>CD «9SOO0C9OD<S><0«<&<&

In 1874 vaccination was introduced into Prussia. Note the decrease in smallpox in the
following year. Vaccination is not compulsory in Austria. The above graphs indicate a direct
relation between the number of smallpox cases and compulsory vaccination.

sented by Pasteur. Jenner, however, collected data from the
people who had had cowpox, and afterward had resisted small-
pox infections. He began the scientific investigation of inocu-
lation. A dairy maid on a certain farm contracted cowpox.
Jenner took some pus from a sore on her hand and inoculated a
little boy with it. The boy became slightly ill, but soon recov-
ered. Later the boy was exposed to smallpox and even inocu-
lated with smallpox virus, but he did not contract the disease.
Evidently the cowpox infection had given him a protection
against smallpox. Jenner made many such experiments and pub-
lished his discoveries in his celebrated pamphlet An Inquiry into
the Causes and effects of the Variolae Vaccinae.
The inoculation with cowpox was called vaccination (vacca —

NATURE AND SYMPTOMS OF SMALLPOX 423

cow). There was a storm of protest against this method of inocu-
lation. Newspapers printed bitter attacks and said people would
show the characters of cows if they had this filthy material from
a cow introduced in them. The results, however, were so successful
that vaccination was gradually accepted as the. only means of con-
trolling smallpox, and the old method of inoculation was soon
forbidden. Napoleon had all his soldiers who had never had
smallpox vaccinated. The Empress of Russia urged its practice
in Russia. Spain and Sicily also introduced vaccination.

About 1800, at a meeting of the American Academy of Arts and
Sciences, presided over by the President of the United States,
John Adams, the introduction of vaccination into America was
first considered. A supply of vaccine material was secured, and
a Dr. Waterhouse vaccinated his five-year-old boy. He afterward
vaccinated other members of his family. They became immune
to smallpox infection. Later Thomas Jefferson became interested
and he had the members of his family vaccinated. From that
time on the practice of vaccination spread rapidly through the
country. The vaccine virus tends to stimulate certain cells of
the body to produce substances known as anti-bodies which re-
main in the blood as a protection against disease. When a vac-
cinated person is exposed to smallpox, he is already fortified by
the anti-bodies which will act against the smallpox bacteria.

Nature and symptoms of smallpox. Smallpox mortality is 30
per cent greater among unvaccinated than among vaccinated
persons. Children are particularly susceptible. In the Montreal
epidemic of 1885-1886, 2717 of the 3164 deaths were children
under ten years of age.

Smallpox is caused by a filterable virus. About three days
after becoming ill with smallpox, little abscesses or pustules
form. If the pustules are deep, affecting the dermis seriously,
pits or pock-marks will always show on the skin. The scales
and crusts from the healing pustules are highly infectious, as are

Number of Cases and Deaths from Smallpox in the United States

1921 1923 1925 1927

Cases Deaths Cases Deaths Cases Deaths Cases Deaths

1. Alabama

2. Arkansas

3. Arizona

4. California

5. Colorado

6. Connecticut

7. Delaware

8. District of Columbia

9. Florida

10. Georgia

11. Idaho

12. Illinois

13. Indiana

14. Iowa

15. Kansas

16. Kentucky

17. Louisiana

18. Maine

19. Maryland

20. Massachusetts

21. Michigan

22. Minnesota

23. Mississippi

24. Missouri

25. Montana

26. Nebraska

27. Nevada

28. New Hampshire

29. New Jersey

30. New Mexico

31. New York

32. North Carolina

33. North Dakota

34. Ohio

35. Oklahoma

36. Oregon

37. Pennsylvania

38. Rhode Island

39. South Carolina

40. South Dakota

41. Tennessee

42. Texas

43. Utah

44. Vermont

45. Virginia

46. Washington

47. West Virginia

48. Wisconsin

49. Wyoming

108,135 764 31,782
* U. S. P. H. Reports. ** Reported by state,
t Compiled by the American Association

424

2072

323

4285

1242

481

315

—

168

192

100

117

5581

2029

4921

984

2606

—

**o

1351

227

207

1356

2191

673

444

1853

*857

155

526

759

8536

937

1625

4809

1910

2996

4809

5204

668

664

1279

4630

483

311

1392

**2367

**n

228

1040

1762

1421

692

883

284

118

214

4537

2311

784

1469

9375

1950

973

198

126

2161

292

. . -

___

**2982

189

*667

1466

732

376

575

3048

831

691

235

*10

255

189

110

631

392

286

376

2513

3352

1920

1777

445

204

208

7286

2415

4018

1558

1393

1184

775

1644

1596

837

859

1167

212

183

—

205

1084

1500

915

559

1959

251

265

403

2913

1037

___

1781

669

1309

2341

3499

168

177

255

1873

541

268

977

4441

1623

2004

1806

2442

*253

821

1099

5216

1338

1517

131

938

434

—

184 36,937 69932,102 138
—-Information lacking,
for Medical Progress.

PREVENTION OF SMALLPOX

425

the contents of the pustules. If the disease is severe, the eyes,
ears, and kidneys may be irreparably damaged. Recovery from
one attack of smallpox usually leaves the individual immune ±o
all subsequent attacks.

Spread. Smallpox is very communicable, that is, it is readily
spread by contact. The smallpox virus may enter the body
through the respiratory system, or through the digestive system.
It is carried by discharges from the mouth and nose, or by the
pus and scabs, which may get in food, or on articles used by
patients.

Prevention of smallpox. Because of the extremely communi-
cable nature of smallpox, isolation or quarantine of all patients
is essential. Sanitary precautions of all kinds should be taken
in handling the patients and all the articles used by them. Ex-

^mallpo*
1 924- -V

cosgs

5500

5000

U-500

H-000

5500

&000

£500

fcooo
1500

1000
5oo

Two groups of states have been compared. The chart on the left indicates those states having
compulsory vaccination; the one on the right indicates local enforcement of the law.

tensive education and widespread publicity as to the value of
enforcing vaccination are necessary in order to keep the disease in

WH. FITZ. AD. BIO. — 28 .

426 SMALLPOX AND ITS CONTROL

check. A vaccination against smallpox lasts from five to seven
years. After that time there should be a second vaccination.
The second vaccination may produce immunity for life. By im-
munity is meant the ability to resist disease. All children should
be vaccinated before they are nine months old. Vaccination
during epidemic periods is also wise.

The vaccine for smallpox is prepared by first developing the
causative organisms in the body of young female calves. After
determining that the calves are perfectly healthy, they are
thoroughly cleaned and inoculated with the crusts collected
from the vaccinations of healthy children. Cysts or vesicles are
formed in about five or six days and the contents of these vesicles
are scraped off and ground into dilute glycerine in order to des-
troy all harmful bacteria. This product is then tested several
times, in many ways, for purity as well as for effectiveness. The
material is then put up in small tubes ready for use.

Value of vaccination. The gradual disappearance of smallpox
is due largely to the widespread use of vaccination. In coun-
tries where vaccination is not required, smallpox is still causing
the deaths of thousands of people each year. It is still one of
the main causes of death in China and India. Between the
years 1918 and 1922, India reported 63,553 deaths from this
disease alone. In Russia, between the years 1902 and 1914, over
a million persons became affected with smallpox and over half
a million died of it.

In the Philippine Islands, prior to the occupation by the Amer-
ican Army, it was estimated that more than 40,000 smallpox
deaths occurred annually. Vaccination was introduced by the
Americans in 1905, and has been continued ever since. There were,
in 1903, 18,989 smallpox deaths, but this number has decreased
rapidly until in 1916 only 239 deaths occurred from this disease.
Then the effects of the first vaccinations wore off and people be-
came careless about being revaccinated. This neglect resulted in a

OBJECTIONS TO VACCINATION NOT VALID 427

serious epidemic in 1918. During this year, 60,447 deaths oc-
curred. At this time, only one case developed among the 5422
vaccinated United States troops who were stationed on the Islands.

There are still about 70,000 cases of smallpox in the United
States annually, because vaccination is not universally enforced.
In two states where vaccination is not required, there are many
cases of smallpox. In one of these states there were over 2000
cases and 230 deaths reported in 1926 ; in the other, 2413 cases
and 31 deaths were reported in 1926. Contrasted with these
states, a state where vaccination is rigidly enforced had, in the
same year, only 56 cases and no deaths.

Objections to vaccination not valid. When there is a specific
prevention for a disease, as there is in vaccination against smallpox,
it seems unbelievable that there are so many cases each year.
The objections raised to vaccination are not well founded. One
of them is that it causes lockjaw. There is no evidence to sup-
port this belief. Since there is a scratch made in the vaccination
process, there is probably the same danger of getting lockjaw as
there would be from any scratch. There is no danger of lockjaw
peculiar to the vaccination process. Strict government inspec-
tion of the virus used in vaccination precludes the possibility of
contamination. Ordinary precautions of a vaccination must be
taken, however, to prevent infection. Some people think the
vaccine is taken from a person who has smallpox and that this
material may contain germs of the disease. The material is taken
from calves and not people. The calves are examined carefully
so as to eliminate the possibility of any disease being transmitted
to people through the vaccine. The vaccine virus is always very
carefully purified before being used.

Questions and Suggestions

1. Trace the early history of smallpox, including its introduction
into America.

2. Trace the history of inoculation to the time of Edward Jenner.

428 SMALLPOX AND ITS CONTROL

3. Discuss the investigation and acceptance of vaccination for the
prevention of smallpox.

4. Give a report on the life and works of Edward Jenner.

5. Discuss the nature of smallpox. How is smallpox spread ? -

6. What are the chief preventive measures against smallpox ?

7. Discuss some of the methods of inoculation used in the past.

8. Has smallpox been checked to the fullest possible extent ? Give
several reasons for" your answer.

Supplementary Readings

Broadhurst, Jean, How We Resist Disease (J. B. Lippincott Co.).
De Kruif, P. H., Microbe Hunters (Harcourt, Brace & Co.).
Haggard, H. W., The Science of Health and Disease (Harper & Bros.).
Pamphlets published by the Metropolitan Life Insurance Co., New York

City.
Zinsser, Hans, A Textbook of Bacteriology (D. Appleton & Co.).

CHAPTER XLII

RABIES AND
ITS CONTROL

Keystone View Co.
Jupille battling with a mad dog.

Keystone View Co.
Interior of Pasteur Institute,
Paris.

How did Louis Pasteur control rabies ? Why does rabies still ex-
ist? What advice did Louis Pasteur give to medical students?

History of rabies. Rabies or hydrophobia is a very ancient
disease. People termed it hydrophobia because a person bitten
by a mad dog develops a fever and a thirst ; yet the attempt to
drink water produces such painful convulsions that he develops a
dread of water. Aristotle thought that man was not subject to
rabies. Pliny the Elder recommended the livers of mad dogs as
a cure. Galen advised a compound of crayfish eyes. Sea bathing
was thought to exert a curative power. In 1780, in France, a
prize was offered to the person who could give the best method for
treating rabies. It was won by a surgeon-major who recom-
mended cauterization or the burning of the infected area with red-
hot irons.

Rabies was one of the dread diseases of the past. People were
so terrified of victims that had been bitten by mad dogs or wolves
that they frequently strangled or suffocated them. They were
afraid of contagion in nursing a case of rabies, since all knew that
rabies meant certain death. A law was passed in France in 1810
prohibiting the murdering of people suffering from rabies.

429

430 RABIES AND ITS CONTROL

Pasteur (1822-1895). About 1882, Louis Pasteur/ a French
scientist, realizing that Jenner and others had successfully immu-
nized persons by vaccination, decided to ar>pl^ the*- same principle
to rabies. He had learned several things about the disease :
(1) that the virus of rabies was contained in the saliva of mad
animals; (2) that it was communicated through bites, and that
the period of incubation varied from a few days to several
months. He thought that there must be some way of prevent-
ing the development of the disease during this long period of
incubation.

Pasteur had examined certain microorganisms in the saliva of a
child that had died of rabies. He thought these were the causative
organisms. When he injected them in animals, however, they
failed to produce rabies. Pasteur inoculated rabbits "with saliva
from rabid dogs. Hydrophobia took months to develop and some-
times did not develop at all. Then he introduced blood from
rabid dogs into rabbits and again was unsuccessful. Pasteur sus-
pected the disease was in the nervous system and believed that
explained the long period of incubation. He took particles of the
brain of an animal that had died of hydrophobia and injected them
into a number of animals. They all developed and died of hydro-
phobia. Evidently, the particles of the brain were more potent
or virulent than the saliva in causing rabies. Pasteur was unable
to use his usual method of investigating disease. He could not
isolate the germ and cultivate it in an artificial medium, because
he could not detect the germ.

Next, he suspended in a sterilized vial a fragment of the brain
of a rabbit that had died of hydrophobia. As the fragment grad-
ually became dry, its virulence or strength decreased until, at the
end of fourteen days, it proved to be harmless when crushed, mixed
with pure water, and injected under the skin of some dogs. The
next day the dogs were inoculated with brain which had dried for
thirteen days. The inoculations were continued, using fragments

PASTEUR

431

of brain of increasing virulence until the brain of a rabbit thaf had
died the same day was used. It was found that the treated dogs
were immune from hydrophobia.

Pasteur invited a commission of
scientists to investigate his work.
Rabid dogs were permitted to bite
healthy dogs that had been treated
with Pasteur's inoculations and
some that had not been treated.
The former did not contract
rabies, the latter did. The scien-
tists were enthusiastic over this
scientific triumph. Pasteur then
showed that the development
of rabies in dogs that had been
bitten by a rabid dog could be
prevented by means of similar
inoculations.

In 1885, a little Alsatian boy,
Joseph Meister, was brought by
his mother into Pasteur's labora-
tory. He had been horribly bitten
by a mad dog. Pasteur, after con-
sultation with other scientists,
decided to give him inoculations
of brain and spinal cord material
that he had prepared. His first
inoculation was material that had
dried fourteen days. This was fol-
lowed by further inoculations, of
increasing strengths. The treatment lasted ten days and included
twelve inoculations. It was successful in preventing rabies and was
the first successful treatment for rabies given to a human being.

Pacific & Atlantic Photos
The people of Chicago have erected a
monument in recognition of the inesti-
mable service of Louis Pasteur to human-
ity. Millions of people passing the monu-
ment give occasional thought to the
nobility of character and devoted life of
the great scientist.

432

RABIES AND ITS CONTROL

Foreign scientists flocked to Paris to learn more about the treat-
ment. Letters came from all over the world for information.
Children were brought from far and near for treatment. From
America, four small children, who had been bitten by mad dogs,
were sent over to Pasteur for treatment. A public subscrip-
tion was conducted by a New York newspaper in order to supply
the funds for their treatments. The inoculations given these chil-
dren by Pasteur were successful. Nineteen Russians who had been
bitten by a mad wolf were brought to Paris by a Russian doctor.
The only French word they knew was " Pasteur." Two weeks had
elapsed between the time they received their wounds and their

arrival in Paris. Although
they were horribly bitten,
all but three of them were
saved.

Pasteur was one of the
first scientists to develop a
method of weakening or at-
tenuating organisms by lab-
oratory procedures for use
as a vaccine. To-day, all
our large cities have Pasteur
Institutes, or similar divi-
sions of the Health Depart-
ment for giving treatment
for rabies.

The nature of rabies.
Rabies is an infectious dis-
ease of dogs, wolves, cats,
and sometimes of horses,
cows, rabbits, and other ani-
It may be communicated to human beings. The infection

2Lry*wi<T

absorbing
CTbteiTiicaTr

Vaccines for the treatment of hydrophobia are
prepared from the spinal cords of animals that have
died from the disease. The cords are suspended
in a bottle which has a water-absorbing material
in the bottom of it. As the cords dry, they become
attenuated or weakened in virulence.

mals.

is from an organism not yet cultivated or positively identified.

THE EFFECT OF RABIES ON ANIMALS 433

It is a filterable virus which attacks the central nervous system.
This virus can be found in the salivary glands and in the saliva of
infected animals. .

If some of the nervous tissue of an animal that has died from
the disease or been killed during the course of the disease be ex-
amined microscopically, characteristic spherical inclusions will be
found. These structures are called Negri bodies and the appear-
ance of them in the brain cells is the principal method of determin-
ing whether or not a suspected animal is rabid. If they are found
in the brain of an animal which has bitten a human being, the
Pasteur treatment is immediately prescribed for the person or
animal bitten. The relation of these Negri bodies to the causa-
tive organism is not yet known. To confirm the diagnosis, a bit
of the brain of the dead animal is sometimes injected into an-
other animal. If the disease is rabies, the second animal will
become sick and die. Because the rabies organism attacks the
central nervous system, the muscles controlled by that system
are secondarily affected and, consequently, paralysis is a charac-
teristic of the disease.

The effect of rabies on animals. When a dog becomes sick
with rabies, only an expert would suspect what the trouble is.
Many cases do not show violent symptoms, although most cases
begin with a characteristic change in the animal's disposition. In
general, the course of the disease is marked by a change in dis-
position, irritability and excitement, which is usually followed
by depression, paralysis, and death.

Transmission. Rabies is transmitted to man by the bite of an
infected animal, because the germs or virus of the disease are in
the saliva. The bite breaks the skin and introduces the causative
organism. There have been cases in which persons contracted
the malady from being scratched by the animals or from allowing
the dogs to lick a hand upon which some scratch or wound
existed.

434 RABIES AND ITS CONTROL

Cure. There is no known cure for rabies once it definitely de-
velops. The only possible help a patient may secure is the pre-
ventive treatment which should be given early.

Prevention. One should always be careful in handling sick
animals, especially dogs and cats. If a dog, suspected of having
rabies, is running loose, it should be penned up for ten days, and
if it does not develop rabies in that time it is safe to let it out.

Most departments of health examine and keep under observa-
tion all dogs suspected of having rabies. They will also take care
of dogs that have been bitten by other animals which are suspected
of having the disease. In order to prevent rabies, the health
departments of many states require that all dogs be muzzled.

To prevent the development of rabies in a person bitten by a
rabid animal, the wound must be washed at once. Under the
care of a competent physician, it should be treated with a strong
antiseptic or be cauterized. Then the preventive vaccination
treatment must be begun at once. This builds up the person's
resistance to rabies. Practically no one has ever been harmed by
this treatment. In all cases, it is of utmost importance to give
the Pasteur treatment immediately.

Large deep bite-wounds are the most dangerous, especially those
about the face, head, back, or any part where nerves and lymphatics
are abundant. A bite through clothing is usually less dangerous
than one on the bare surface.

The eradication of rabies in man depends upon its prevention
in domesticated animals. This problem of prevention still exists
in certain sections of the world, as the disease is very prevalent
among wild animals which transmit it to dogs and other domes-
ticated animals. In 1923, approximately 22,000 persons in the
United States applied for and received the Pasteur treatment.

In England, the enforcement of the law requiring the muzzling
of dogs and a quarantine on all animals imported from other
countries eliminated the disease entirely from 1903 to 1918.

PASTEUR'S IDEALS

435

It is now possible to give prophylactic or preventive treatment
to dogs, which render them immune to rabies. In 1924, approxi-
mately one hundred thousand dogs in
Japan were immunized, and the num-
ber of cases of the disease was reduced
to forty-one. Before that time there
were approximately 1700 cases of rabies
each year among the dogs.

Pasteur's ideals. In closing a chap-
ter that brings in a part of the work
of a remarkable man, no more fitting
tribute can be paid him than to repeat
a part of a speech made to Pasteur on
his seventieth birthday. The great
theater of the Sorbonne was filled by
committees from Denmark, Sweden,
and Norway. The members of the
French Institute and the Professors of
the Faculties were there. Students of

medicine had crowded into every available place. Lister was
there, representing the Royal Societies of London and Edinburgh.
Many offerings were tendered Pasteur, many tributes paid, and
the last was made by the President of the Students' Association,
who said, " You have been very great and very good ; you have
given a beautiful example to students."

Pasteur's voice, weakened by his emotion, could not have been
heard over the large theater. His reply was read by his son :

"... do not let yourselves become tainted by a deprecating
and barren skepticism, do not let yourselves be discouraged by
the sadness of certain hours which pass over nations. Live in the
serene peace of laboratories and libraries. Say to yourselves first :
' What have I done for iny instruction ? ' and, as you gradually
advance, ' What have I done for my country ? ' until the time

A sketch of a brain smear prep-
aration of a suspected " mad " dog.
The presence of nucleated Negri
bodies led to a diagnosis — "rabid
animal." The boy bitten by this
animal was given the Pasteur treat-
ment and did not develop hydro-
phobia.

436 RABIES AND ITS CONTROL

comes when you may have the immense happiness of thinking
that you have contributed in some way to the progress and good
of humanity. ..."

Questions and Suggestions

1. State some of the ancient ideas on the treatment of rabies.

2. Describe Pasteur's experiments with saliva and blood.

3. Discuss Pasteur's experiments with dried brain and spinal cords.

4. Discuss the first vaccination of animals against rabies.

5. Discuss the first vaccination of a person against rabies.

6. What effect did the discovery of vaccination against rabies have
on the world ?

7. What stimulus did Pasteur give later scientists by his work on
vaccination ?

8. Discuss the cause, method of invasion, and symptoms of rabies.

9. Discuss methods of preventing and controlling rabies.

10. What is the importance of vaccination against rabies ?

11. Is there anything in Pasteur's speech that indicates why he has
been called one of the finest scientists the world has ever produced ?

12. Give a report on the life and work of Pasteur.

Supplementary Readings

Broadhurst, Jean, How We Resist Disease (J. B. Lippincott & Co.).
De Kruif, P. H., The Microbe Hunters (Harcourt, Brace & Co.).
Haggard, H. W., The Science of Health and Disease (Harper and Bros.).
Vallery-Radot, Rene, The Life of Pasteur (Doubleday, Page, and Co.).

CHAPTER XLIII

TUBERCULOSIS

AND ITS

PREVENTION

Robert Koch.

Edward Livingston Trudeau.

How was the germ of tuberculosis discovered? Was the discovery of
the tuberculosis germ due to careful scientific investigation ? Is tuber-
culosis a curable disease?

Pasteur presented his germ theory of disease to the world in
1860. At that time many people did not have much faith in his
work, but he cleared the way for much of the work done by other
scientists of his own day and later. The investigation of tuber-
culosis would probably have been impossible had it not been for
Pasteur's work.

Dr. J. A. Villemin. In the nineteenth century, medicine was not
based on scientific research. Pasteur's work on microorganisms
was not accepted generally until the latter part of the century.
In 1864, Dr. J. A. Villemin, one of the few real scientists, by means
of experimental research, brought out the idea that tuberculosis
was a disease which reproduced itself and could be reproduced
only by itself. In brief , he said it was caused by a specific organism,
and could be communicated from one person to another. In
order to demonstrate the fact that tuberculosis was communi-
cable, he experimented on animals. He took some sputum of a
tubercular patient, spread it on cotton wool which he dried and
made into a bed for guinea pigs. The pigs, in time, became tuber-

437

438 TUBERCULOSIS AND ITS PREVENTION

cular. People did not accept Villemin's findings. They still clung
to the idea of spontaneous generation of this and other diseases.
In fact, he was treated as a disturber of medical order and beliefs.

Professor J. Cohnheim, 1839-1884, at Breslau, found that he
could give tuberculosis to rabbits by putting a bit of the tubercular
patient's diseased lung into the front chamber of a rabbit's eye.
Here he could watch the little island of tissue spread and do its
deadly work of building tubercles.

Koch discovers the cause of tuberculosis. Robert Koch (1843-
1910) built on Cohnheim's work. As long as animals could be
inoculated with the disease, he could experiment with them.
At this time, probably, one out of every seven people was dying
of tuberculosis. Koch took tubercles from a man who had died
of tuberculosis and injected them into the eyes of guinea pigs and
rabbits. While he was waiting for them to develop signs of the
disease, he examined tissues of people who had died of tuberculosis.
No microorganisms showed. He stained the tissues with different
dyes, in order to see the germs. (As he worked, he kept dipping
his hands into bichloride of mercury, for Lister, the English sur-
geon, had demonstrated the importance of antiseptics in checking
infections.) Finally, Koch smeared some material from tubercles
of a tubercular person on a glass slide, dipped it in' a certain dye,
and mounted it under his microscope. He saw slender rod-shaped
organisms very minute in size, about 1 5 I of an inch long.
The last stain had been successful.

In the meantime, the guinea pigs and rabbits, which he had in-
oculated became sick and died. He examined their bodies, and
found tubercles which he stained and examined microscopically.
In every case he found the always slender, curved rods. He ex-
amined the bodies of many people who had died of tuberculosis
and always found tubercles. * Then he injected (inoculated) tuber-
cles into guinea pigs, rabbits, dogs, cats, and many other animals.
Invariably all the animals inoculated with the tubercles died of

KOCH DISCOVERS THE CAUSE OF TUBERCULOSIS 439

tuberculosis. As each animal died, Koch examined its tissues and
always found tubercles and the slender rods. Then he examined
tissue after tissue of healthy animals and found no tubercles. _

He was not yet positive that he had discovered the tubercle
bacilli. He decided that he must first cultivate them outside the
body of animals and then introduce the cultivated organisms into
healthy animals. If the inoculated animals became tubercular, it
would indicate the presence of the organisms. He made every
kind of broth then known for the cultivation of germs. He kept
some of his tubes and bottles* at the temperature of the room,
some at the temperature of a man's body, and others at fever
temperature. He infected his broths with portions of the in-
fected lungs of guinea pigs. No tubercular organism grew in
any of the broths, regardless of surrounding temperatures.

Undaunted, he thought he would try tissue extracts for his
media. Possibly tissues had peculiar materials that were essential
for the growth of the tubercle bacillus. He obtained serum from
blood, mixed it with agar, heated it to make it set, and placed it
on slants in test tubes in order to get long, flat surfaces on
which to grow the bacilli. He streaked the serum-agar with a bit
of the infected lung of a guinea pig that
had just died of tuberculosis. Then he
placed his tubes in an incubator at the
same temperature as that of the guinea
pig's body. On the fifteenth day the
serum jelly was covered with tiny glisten-
ing specks. When magnified with a hand
lens, they appeared as dry, tiny scales. <g^— Jn^SSi
He stained and mounted one of the scales The rod-shaped structures,
under the microscope and found the same are'toe bacuit thatVusTtu-
bacillus which he had discovered in the lung t> erculosls -
of tubercular victims.^ He had grown tubercle bacilli outside the
body of an organism. He then inoculated animals with the bacilli

440 TUBERCULOSIS AND ITS PREVENTION

grown on his serum-agar; the inoculated animals contracted
tuberculosis and died.

He decided to try one more experiment. He wondered how
people contracted tuberculosis, and thought that they had prob-
ably inhaled some of the dust particles of which Pasteur had
spoken, or possibly were infected by droplets which tubercular
people scattered in the air when they coughed. He sprayed
bacilli into the air breathed by certain animals. The animals
became tubercular and died.

The method of investigating an unknown disease that Koch
used in 1882, is still being used to-day. His method is commonly
known as Koch's postulates which are : (1) isolate the probable
germ from the diseased organism ; (2) grow the germs in an arti-
ficial media; (3) transfer the germs from the culture to an
organism and notice whether they will produce the disease;
(4) obtain some of the germs from the second organism and iden-
tify them. From Koch's investigation, dates the beginning of the
triumph of bacteriology.

Koch reported his findings before the Physiological Society, in
Berlin, in March, 1882. The most brilliant men of science in
Germany were there. There was no word of criticism against
his work ; it was too thorough and convincing. The news of his
discovery spread rapidly, and the entire world soon learned of his
work and his methods of investigating diseases.

Edward Livingston Trudeau. While Koch was investigating
the cause of tuberculosis, there was a man named Trudeau living
in the United States. , He was taking care of a tubercular brother
whom he bathed, fed, and even slept with. His doctor warned
him not to open the windows as it was bad for the brother's cough.
The brother finally died.

Trudeau then studied medicine, became a doctor, but did not
practice long, before he realized that he had tuberculosis. Like
all people of his day, he thought tuberculosis meant certain death.

EDWARD LIVINGSTON TRUDEAU

When he realized that he had tuberculosis, he went to end his
days in the Adirondack Mountains which he loved. Strangely
enough, his health be-
gan to improve. Two
or three doctors, hear-
ing of his improvement,
sent other tubercular
patients to him and a
small sanitarium was
thus started in the
northern part of New
York State. Trudeau
heard of Koch's work
and went back to New
York city to learn the
laboratory methods of
isolating the tubercle
germs. Then, return-
ing to the mountains,
he started experiment-
ing on rabbits. He
took three sets of rab-
bits. He inoculated two
of them with tubercle
bacilli. One of these
sets he placed in a dark
camp box that was
poorly ventilated, and
gave them an insuffi-
cient diet. The other that had been inoculated he let roam on
an island in the Adirondacks where there was plenty of air, sun-
light, and food. The third set, that had not been inoculated,
was also put in very unfavorable surroundings. The results were

WH. FITZ. AD. BIO. — 29

TUBERCULOSIS-ALL FORMS

Prospective deathrates, l$)2d to 1937

Original Registration States and District of Columbia

DEATHRATE DEATHRATE
PER 100,000 PER IOO.OOO

200
100
160
140
120
100
00
60
40
20

200

- 160

■ 140

■ 120

- too

-60
■60

' 40

fco

. UJ.I.

1 1 1 1

I I 1 I

nit

llll

\
lilt

I9<

30 1905 1910 1915 1920 1925 I5J0 1955

YEARS

SJ7

If the trends between 1900 and 1922 are averaged, the
expectation of the tuberculosis death rate for 1937 is about
40 per 100,000. If the decrease of 1926 and 1927 con-
tinues, the death rate in 1937 would be 20 per 100,000.
A greater decrease than has yet been shown is necessary
to bring the death rate to 0. (From Health and Wealth by
Dublin, Harper & Bros.)

442 TUBERCULOSIS AND ITS PREVENTION

that the rabbits living in the good environment recovered from
the effects of the inoculation. The inoculated rabbits living in
poor conditions died within three months from tuberculosis. The
rabbits that had not been inoculated but were in the poor envi-
ronment did not show tuberculosis, although they were not in
good physical condition. Repeating similar experiments, he proved
that unsanitary conditions, alone, will not cause tuberculosis ; the
germs must be there. He also showed that unfavorable envi-
ronments favor the development of tuberculosis and good living
conditions help to check the disease.

Trudeau, with the help of another doctor, started his sanita-
rium at Saranac Lake. He built a number of small cottages and
thus started the Cottage Plan of Tuberculosis Sanitariums. He
enforced a routine which included plenty of fresh air, rest, good
food, and sunlight. This method was revolutionary. Trudeau
was the first physician in the United States to teach the impor-
tance of fresh air in the treatment of tuberculosis. Since his
time numerous sanitariums have been built over the entire world.

Causative organism. A rod-shaped bacillus is the cause of
tuberculosis. There are many types of these bacilli. They
attack practically all warm-blooded animals. Most of the tuber-
culosis among children under five years of age is of the bovine
type. It is the type that attacks cattle and usually is taken in
by the child with milk.

The bacilli of tuberculosis may attack any part of the body but
once present the germs are very likely to eventually attack the
lungs. They actually feed on and destroy lung tissue. They
form little nodules or tubercles filled with a cheesy material and
produce poisons or toxins. There is always a toxin called an en-
dotoxin produced within the bacillus and probably an exotoxin,
an excretion, is given off. A slight tubercular infection almost
always occurs in childhood. The normal resistance of the child's
body overcomes the disease by either killing the bacilli or keeping

CAUSATIVE ORGANISM

443

them from growing. In the latter case the germs are still alive
and will become active again, whenever the resistance is weakened

REGIONAL INCIDENCE OF TUBERCULOSIS MORTALITY
IN THE UNITED STATES

Adjusted* Deathrates per IOQOOO. Tubercubsis-all forms. 1922

WHITE POPULATION**

State Pate

COLORADO 112.6

CALIFORNIA 144 5

TENNESSEE 121.6

KENTUCKY 121.6

OELAWACE 115.9

MARYLAND 969

> NEW YORK 930

'RHODE ISLAND ©15

VIRGINIA SI.4

HEW JERSEY 91.2

MISSOURI 9Q7

CONNECTICUT ©06

MASSACHUSETTS 9Q0

VERMONT 67 fl

PENNSYLVANIA 67.7

NEW HAMPSHIRE 666

INDIANA 646

OHIO 61.6

MAINE 61.2

ILLINOIS 60 1

NORTH CAROLINA 79.7

WASHINGTON 75.0

LOUISIANA .737

WISCONSIN 70.0

hats-* o » »o iso 200 m 100

WHITE POPULATION**

Stato

OREGON

MINNESOTA

MICHIGAN

FLORIDA

MONTANA

SOUTH CAROUNA

MISSISSIPPI

KANSAS

UTAH

NEBRASKA

100 150 200 ISO WO

* Pates adjusted for differences of sex and aie constitution of population.

* * Includes States with populations containing number or proportion of colored
persons insufficient to warrant separate tabulation.

Make a graph from the latest figures of your own and neighboring states and compare it
with this chart. Give the possible reasons for a high mortality among the colored population.
(From Health and Wealth by Dublin, Harper & Bros.)

by infection, malnutrition, overwork, and fatigue. Data concern-
ing the prevalence of tuberculosis in childhood and the subsequent
recovery of the children from it is known, because investigation
proves that the lungs in practically every dead body examined
and the X-rays of living lungs show old scar tissue. The scar tis-
sue is characteristic of tuberculosis attacks. Bacilli that get into
the blood are frequently carried to a lymph gland, where white
corpuscles in great numbers attack and destroy them. The body,
meanwhile, builds a hard wall of 'lime salts around the infected
gland, so that the infection is thus removed from the circulation.
Sometimes infected glands are cut out to prevent the spread of
the germs. Tuberculosis is not hereditary, but susceptibility to

444 TUBERCULOSIS AND ITS PREVENTION

the disease is probably inherited. People who know there is a
history of tuberculosis in the family should be especially careful to
live very hygienically. When this is done, they are not likely to
contract the disease. Poor environment is a predisposing cause of
tuberculosis. If a mother has contracted the disease, her child is
likely to live in the same environment and will probably contract
the disease. For the good of the child, it should be taken from its
parents in such cases, so that it can build up a strong resistance.

Symptoms of tuberculosis. The symptoms are several. Fever,
especially in the afternoon, even in earlier stages before coughing
has started, habitual coughing and spitting, poor appetite, faulty
digestion, and steady loss of weight are usually indicative of an
infection.

Diagnosis. Diagnosis consists of a microscopic examination of
the sputum for the bacilli. A careful examination of the general
physical condition including an X-ray examination of the lungs
is made. The X-ray photograph will show any scar tissue. A
tuberculin test is sometimes made. This is given by putting toxins,
squeezed from tuberculosis germs, under the skin of the suspected
patient. If the disease is present in the patient, there will be an
increase in fever and pulse, an increase of inflammation of the
affected part, and a redness at the- point of infection. A nega-
tive test is conclusive proof of the absence of the disease. A
positive test may indicate a past as well as a present infection.
Since a positive reaction may be obtained from nearly every
adult, the test is chiefly valuable, for young children.

The tuberculin test for cattle has been used for years. Accord-
ing to laws in some states, state inspectors test the dairy cows.
When the test shows the presence of the disease, the cow is killed
and the farmer is partially reimbursed for the loss. All states
do not have this law. Some states have such laws, but let the
townships decide whether or not they will be enforced.

Spread of tuberculosis. Tuberculosis is spread in innumerable

SPREAD OF TUBERCULOSIS

445

ways. Two modes of entrance of the germs into the body are
through inhalation to the lungs and through ingestion to the ali-
mentary tract, and thence to the lungs. The disease may^be
actually spread from person to person by : (1) spray thrown out
in coughing and sneezing, a droplet method of infection ; (2) con-
taminated objects, such as drinking cups and pencils, handled or
used by a tubercular person; (3) personal contact, such as kiss-
ing and handshaking, with an infected person ; (4) food infected
by being coughed on or handled by a tubercular person ; (5) dust
from street or car, containing dried sputum of a tubercular
patient ; (6) houseflies carrying tubercular germs on their bodies
may crawl over and infect food ; (7) milk and butter of tuber-

TUBERCULOSIS AND OCCUPATION

Percentage, Phthisis Deathrate in Specified Occupation
of Deathrate among Farmers. England and Wales, 1910- 1912.

OCCUPATION

PERCE

Tin miners

12000

Cutlers, scissors makers

617.5

File makers

1614

Barmen

161.4

Peddlers

1386

Sandstone-masons

126.1

Lead miners

561.7

Potters-earthenware mfr.

494.7

Laborers (unspecified)

461.4

$eamcn.etc(merchant service

' 456.1

Stone-masons

4156

Brass and bronze workers

4066

Shoemakers

369.3

Printers

366.4

Hotel keepers, saloon keepers

341.4

Vjkh and dockmafers. jewelars

326.1

Tailors

326.1

Glass manufacture

3226

Hatters

321.1

Furriers

319.3

Brewers

311.5

* t » 10 I i

OCCUPATION
Clerks

Painters, decorators
Copper workers, coppersmiths
Kach inists. boiler-fnahers. milrwrighb
Carpenters. Joiners
Bricklayers

Domestic coachmen, grooms
Vfeol. worsted manufacture
Cotton manufacture
All storekeepers
Shipbuilding
Coal miners

Stationary engineers and firemen
lron-miners,quarriers *
Brick,plain Ue.terra-cotta makers
ApVicultural laborers
Builders

Motor car drivers
Railway engine men
Farmers, graziers, etc.

PERCENT,
210.2
266.4
236.1
231.6
224.6
U4.6
211.5
211.5
210.5
203.3
166.1
133.3
133.3
126.1
126.1
1246
121.1
105.3
100.0
I00.O

KKCMT A KVHOBCDS —

Compile figures for your own country, state, or city and compare them with this table.
(From Health and Wealth by Dublin, Harper & Bros.)

cular cows. (The tuberculin test shows that 15 per cent of the
cows of to-day are infected with tuberculosis.)

446 TUBERCULOSIS AND ITS PREVENTION

Treatment. Since the body itself must fight this disease, it
should be given the best possible environment under which to
work. Giving the patient the most healthful conditions is the
most we can do for him. Fresh air, sunlight, plenty of sleep,
freedom from worry or work, and an abundance of easily digested
food such as milk and eggs are the main factors in the treatment.
Outdoor treatment is usually best if the climate is mild. It is best
and most always necessary to have expert treatment at a sanita-
rium under the supervision of a doctor, for at least six months.

Prevention. . There are a number of measures to be observed
by individuals in order to prevent infection : keep the resistance
of the body high by proper living habits ; have a general physical
examination once a year ; teach or compel all tubercular persons to
cover their mouths with handkerchiefs when coughing ; use paper
cups and paper towels in public places and use only sanitary
drinking fountains ; keep the dust down, by using a vacuum
cleaner and damp cloth in the home, and by sprinkling and flushing
the streets ; keep flies out of the house by screening the doors and
windows, and off the food by covering it ; report all cases of
tuberculosis not under proper medical care to the Board of Health.
The communities can also help to control the spread of tubercu-
losis. They should require the inspection and pasteurization of
all milk. Only raw milk from tuberculin-tested cows should be
sold. They can also aid by enforcing the existing laws against
spitting in public places ; requiring Board of Health certificates
from the persons who handle foods ; providing for healthful living
conditions in tenement houses ; and providing for more hospitals by
fostering the sale of Christmas seals. Probably one of the most
important ways of controlling the disease, is to educate the peo-
ple against the dangers of tuberculosis and the best methods of
preventing it.

The tuberculin test was first devised by Koch in 1890. People
kept insisting that he find a cure for the disease, since he already

PREVENTION

447

knew the cause of it. He was working on a tuberculin inoculation
which could be introduced into people as a means of working up a

International Newsreel
Fresh air is invaluable in treating tuberculosis. Some sanitariums require patients to dress
as lightly as possible, even in winter. The exposure of large areas of the body to air and
sunlight is helpful in the treatment of tuberculosis.

"resistance or an immunity. He was literally forced into publish-
ing his work before he had tested it sufficiently. Doctors began
to inoculate people with the tuberculin test devised by Koch. In
many cases the results were fatal. Tuberculin inoculation then
fell into disrepute.

At present, a group of doctors is working on a tuberculin vac-
cine at the Pasteur Institute in Paris. The vaccine consists of

448 TUBERCULOSIS AND ITS PREVENTION

greatly weakened germ material. It is hoped that this will stim-
ulate the body to make protective materials which will stay in the
blood. If the vaccinated person then comes in contact with the
active disease, he is already fortified and protected and should not
contract the disease. In France, the average mortality among
infants from tuberculosis is about 20 per cent. In a recent scien-
tific experiment 969 infants who were born of tubercular mothers
or were in direct contact with the disease were inoculated.
Among the vaccinated infants, for the two years following vac-
cination, the mortality for this disease was about one per cent;
the mortality was nil after two years. The resistance lasted more
than four years. Hence the infants were immunized or protected
for the period when tubercular infection is most dangerous.

Prevalence and economic importance. It is estimated that
tuberculosis causes one tenth of all the deaths in civilized coun-
tries ; until recent years it was the principal cause of all deaths.
There are one million, five hundred thousand cases of active
tuberculosis in the United States ; one hundred and fifty thousand
deaths occur every year. The mortality, therefore, is approxi-
mately ten per cent. There are probably twice as many deaths
every year from the tubercle bacilli as there were among our
military forces during the World War.

The disease is estimated to cost the United States $225,000,000
a year. The mortality was reduced from 224 for every 100,000
people in 1911 to 114.2 in 1922, a reduction of 49.2 per cent. In
1928 the deaths from tuberculosis were the lowest on record.

Questions and Suggestions

1. What was the contribution of Dr. Villemin to the investigation
of tuberculosis ?

2. Discuss the experiments of Koch.

3. Name Koch's postulates.

4. Look up and give a report on the life and work of Koch.

PREVALENCE AND ECONOMIC IMPORTANCE 449

5. What was Trudeau's contribution to the investigation of tuber-
culosis ?

6. Give a report on the life of Edward Livingston Trudeau.

7. Discuss the cause, method of entering the body, part of organ-
ism attacked, and effect on the body of the tubercle bacilli.

8. Discuss the diagnosis of tuberculosis in people and in cattle.

9. Name all the ways by which tuberculosis may be spread.

10. What is the treatment for tuberculosis ?

11. What precautions should be observed in order to eradicate
tuberculosis.

12. What is the status of tuberculin vaccinations at present?

13. Is tuberculosis increasing or decreasing? Is it sufficiently
under control ?

Supplementary Readings

Broadhurst, J., How We Resist Disease (J. B. Lippincott & Co.).
De Kruif, P., Microbe Hunters (Harcourt, Brace & Co.).
Greaves, J. E. & E. O., Elementary Bacteriology (W. B. Saunders Co.).
Haggard, H. W., The Science of Health and Disease (Harper & Bros.).
Zinsser, Hans, A Textbook of Bacteriology (D. Appleton & Co.).

CHAPTER XLIV

DIPHTHERIA,

SCARLET FEVER,

AND TETANUS

Tetanus bacilli.

Diphtheria bacilli.

Can diphtheria be completely eradicated"? Is there any protection
against scarlet fever ? What is the relation of tetanus to wounds?

Three diseases that are somewhat similar in their methods of
attacking the body are diphtheria, scarlet fever, and tetanus.

History of diphtheria. Fairly accurate descriptions of diph-
theria have been given by certain ancient Greeks. There is evi-
dence that the disease has been known for many centuries. In
1826, a scientist in France was the first to look upon diphtheria as
a specific and infectious disease that was frequently spread by
the use of a common drinking cup. He said that croup was a
type of diphtheria, and he differentiated the disease from the
sore throat of scarlet fever.

Isolation of organism. Klebs, in Germany, in 1883, discovered
bacilli, striped with bars or bands, in the throat of children sick
with diphtheria. In 1884, some banded bacilli were isolated and
stained with methylene blue by Emil Loeffler, who thought that
they could not be the causative organisms of diphtheria. He
was confused by the fact that some perfectly well children had
these bacilli in their throats and some children who were ill with
what seemed to be diphtheria did not have the germs. Loeffler
grew the banded bacilli on broth and injected them under the
skin of guinea pigs. The pigs died, although the bacilli did not
spread, but stayed at the point of entrance below the skin.

450

ISOLATION OF TOXIN 451

Isolation of toxin. In 1888, Roux and Yersin showed that the
diphtheria bacillus produces a toxin. Roux had realized that
the germs might secrete a deadly toxin which he attempted -to
separate from the germs. He grew the bacilli on broth and used
a porcelain filter that held back the germs, but permitted the
soluble material to pass through. The filtered liquid was then
inoculated into guinea pigs which developed the symptoms of
diphtheria. Thus Roux showed that the diphtheria bacilli kill
through a toxin rather than by the spread of the germs. Earl'er
investigators of this disease were unsuccessful because they did
not realize that the germs stayed in the throat and sent out
toxins (exotoxins) which affected the body. The healthy people
who had diphtheria germs were probably diphtheria carriers and
the sick people who did not have the bacilli in their throats
probably did not have diphtheria.

The discovery of antitoxin. The toxic effects of the diphtheria
bacillus led Von Behring to believe that blood contained certain
chemical substances which would kill invading microbes without
injuring the person or animal. After a series of experiments,
he finally inoculated diphtheria toxins under the skin of guinea
pigs that had recovered from diphtheria.
They were not affected by the toxins, but
when he inoculated toxins under the skin
of guinea pigs that had not had diph-
theria, they became ill.

Von Behring obtained blood from guinea
pigs that had recovered from diphtheria,
separated the serum, and mixed it with Bacterium cUphtheriae
diphtheria toxin. He injected this mix- The beaded appearance,
ture of serum and toxin into healthy ^^^^
guinea pigs and they were not injured by carefull y p^pared culture,
it. But, when he mixed blood serum from guinea pigs that had
never had diphtheria with diphtheria toxin, and inoculated the

452 DIPHTHERIA, SCARLET FEVER, AND TETANUS

mixture into healthy guinea pigs, they died. From these experi-
ments, he concluded that guinea pigs which had contracted and
recovered from diphtheria had something in the serum that safe-
guarded them from subsequent attacks of the disease. He called
this protective material antitoxin. His experiments showed that
the guinea pig's body made protective antitoxins to combat the
toxins of bacilli. These antitoxins remained in the blood of
animals that recovered from diphtheria.

He then decided to prepare an immune serum which would
protect babies. He injected small amounts of diphtheria toxins
into sheep and continued to give them doses of increasing strength.
Ultimately, the sheep were immune to the most powerful diph-
theria bacilli. Then he injected serum from the immune sheep
into guinea pigs and later he inoculated diphtheria bacilli into
these pigs. They were not affected by the bacilli. Evidently,
the antitoxins made by the sheep's body were effective in pro-
tecting the guinea pigs against diphtheria bacilli. One serious
difficulty was that this immunity did not last. In 1891, Von
Behring discussed the use of serum on babies, and in 1893 it
was first used in the Children's Hospital in Berlin with some
degree of success.

The discovery of active immunity. The fact that sheep, goats,
and horses used in the production of antitoxin seemed to develop
a permanent immunity to the diphtheria toxin gave the basis for
the next step in this work. Persons who had once been sick with
diphtheria seemed to be free from further attacks. This gave
support to the idea that the presence of toxins stimulates the
human body to produce its own antitoxins. The action of the
body in producing its own protective material is known as active
immunization, and the resulting condition is active immunity.

Investigators mixed antitoxin with toxin and found that the
toxin was rendered harmless. Von Behring was the first to
attempt to give a permanent immunity to children by means of

A TEST FOR IMMUNITY

453

this mixture, but his work was interrupted by the World War.
Later, Dr. William H. Park of the New York City Laboratories,
inoculated children with the antitoxin and toxin, known as toxin-
antitoxin, and was successful in having them develop an active
immunity which was permanent.

A test for immunity. In 1913, Dr. Bela Schick devised the
Schick test of susceptibility. When small quantities of toxin are
put under the skin of children, the reaction will indicate whether
the child is naturally immune or not. If naturally immune, the
toxin will be neutralized by antitoxins in the blood and no effect
is produced. If not immune, a slight local irritation results in
the form of a red spot which appears and disappears within a def-
inite time period. It indicates that there are not sufficient anti-
toxins in the blood to neutralize the small amount of toxin injected.

Cause of diphtheria. Diphtheria (sometimes called " mem-
branous croup ") is justly regarded as one of the most dreaded of
the diseases of childhood. It is a disease of temperate climates,
occurring most frequently in the colder months. In cities, the
disease is always more or less prevalent ; in rural communities, it
is more likely to occur in
epidemics.

Deaths from diphtheria
occur chiefly among chil-
dren less than five years
old. There is a definite
increase in susceptibility
to the disease during the
first two years of life,
and a gradual develop-
ment of immunity there-
after, especially if the
individual lives in a well-
populated district and is more or less exposed to the disease.

AGE GROUPS

•un&ef 3 •morvtKs
3to6 'mont'hs

6 tooths to ly**.

1 -*© ayewv

2 -fe 3 ye<xr*s

3 4o 3 VGcers

lO*© 2oVea/r&

over aoVeart

$u$ceptibility

36 1

<*OJ

7o]

"Htoj

r.,3Pi

_*d

Am. Ass. for Med. Prog.
Note that the ages of greatest susceptibility to diph-
theria is among the pre-school children group. This
is where the greatest prevention work should be done.

454 DIPHTHERIA, SCARLET FEVER, AND TETANUS

&aa£hS'T>et*
•loo.ooo
population
HO

DlPWf HEPIA. Tnust g>
f romTfesf ybrfc State

Diphtheria is caused by the growth of the diphtheria bacillus,
usually in the throat, nose, or larynx. This germ is a slender,
slightly curved, club-shaped rod, which does not form spores,
and which, when stained, shows characteristic staining particles.
These particles make the stained organism easily recognized.

Effect on the body. The diphtheria bacilli grow in the affected
part (throat or trachea usually) and first cause inflammation and
swelling, and later form a grayish membrane. The bacilli multiply
in the membrane and at the same time throw off virulent toxins
which will cause death when absorbed by the body in sufficient
quantities. If the membrane grows down sufficiently into the
trachea, death may occur from suffocation. The action of the
toxin on the heart is particularly severe and sometimes brings about
heart defects, even after the patient has become convalescent.

How diphtheria is
carried. Each new
case of diphtheria is
derived from a previ-
ous case of diphtheria
or from a diphtheria
carrier. The disease
may be spread from
infected to well per-
sons by direct contact,
as by kissing or by
mouth spray given off
in sneezing or cough-
ing. The germ-laden
droplets of such mouth
sprays may enter the
mouths of others or
be breathed in with" the air, or they may be carried to the mouth
from the hands in eating. Indirectly, the bacilli may be trans-

laas •89 , 9TOT9S'97 '900 'MWoB KiT*V> , l& SO 22 '24 '26 "IS, '3Q

Diphtheria is a disease that can be completely controlled
through scientific measures. It has been estimated that
the cost of treating one case of diphtheria will protect two
hundred children from the disease. Note the effect of anti-
toxin and toxin-antitoxin on the death rate in New York
State.

TREATMENT

455

compare your-
town cDithL'

cases AUBVRN.XX
97

<mly one
«*^« aeathfrom.

DlPHttfERIA

from
1324 to 1^29

19*2 19%

mitted through the agency of various objects such as pencils,
apples, candy, eating utensils, drinking cups, or the like, which
have been handled or used
by infected persons. Diph-
theria carriers are seem-
ingly well individuals who
harbor the bacilli in their
bodies. Persons who have
been in contact with those
suffering from diphtheria
are especially likely to be
carriers, yet a certain per-
centage of the population
of any community may

be found harboring the The record of Auburn, New York, is one that can be

A mh +>. Pria ffPrm <? p 1 th m 1 trh attained in all towns. Diphtheria can be eradicated if

aipntnena germs, aitnougn proper prophylactic mea sures are taken,
unaware of having been

exposed to any case of diphtheria. The germ of this disease
grows freely in milk. As this food undergoes so much handling
during production, the germs of diphtheria often have an oppor-
tunity to get into milk unless great care is taken.

The diphtheria germ is easily killed by ordinary disinfectant
solutions and is rather easily killed by drying. When it is con-
tained in pieces of membrane, it may live for some time. Heat
quickly destroys the germ, but temperature as low as freezing is
not fatal to it.

Treatment. The communicability of diphtheria renders impera-
tive the strict isolation of patients. Unnecessary furniture should
be removed from the room, and that which is left should be of a
kind easily cleaned. Separate linen and utensils of every kind
should be provided for the exclusive use of the patient. Such
materials should be boiled, or, better, treated with a powerful
germicide after use. The attendant nurse and the physician

456 DIPHTHERIA, SCARLET FEVER, AND TETANUS

should be the only persons in contact with the patient. After
handling the patient, which should be done as infrequently as

possible, the hands
of the attendants
should . be immedi-
ately cleansed in a
germicidal solution
and then washed with
soap and water.

Diphtheria anti-
toxin is usually ad-
ministered early to
help the patient get
control of the disease.
This antitoxin pro-
duces immunity with
little or no work on
the part of the cells

The strength of the toxin is tested by injecting a very small „ , , , .

volume into a 250-gm. guinea pig. If the pig dies within four 01 the patient S body,

days, it is toxic enough to inject into a horse to produce q •• . ...

antitoxin. After a given time, blood is drawn from the horse, oUCh immunity IS

the serum with its antitoxin is separated from the blood and U rir4 ,, rr , QC Q c " , p

again tested. This time, a little serum is mixed with some Known ab pdSblve

toxin and the mixture injected into a guinea pig. If the pig i m m n n t + v Wh p n

lives, the serum is shown to contain antitoxin and will be eff ec- immunity. " ucu

tive. Look up the exact amounts of material and time in- -fc\iQ antitoxin neU-
volved in this standardization process.

tralizes the toxins of
the invading germs, the patient's body develops its own anti-
toxins. This results in an active, permanent immunity. The
administering of a sufficient quantity of antitoxin is the primary
remedy for the cure of diphtheria. When a physician is not
called early enough, the case may advance so far that the ad-
ministration of antitoxin is valueless. Too much toxin has then
been produced by the invading germs for the antitoxin to v neu-
tralize. If other members of the family are in contact with the
patient and have not been immunized by the toxin-antitoxin

THE APPLICATION OF THE SCHICK TEST 457

mixture, it is always advisable to give them an inoculation of anti-
toxin, which will produce an immediate immunity for a short time.

The application of the Schick test. By means of the Schick tests
it is possible to determine which individuals possess immunity to
diphtheria and which individuals are susceptible, that is, are likely
to contract diphtheria if exposed to the germs. If a child is
found to be susceptible, he is rendered immune by injections of
toxin-antitoxin. This stimulates the body to produce its own
antitoxins and thus establish an active immunity.

The Schick test and the subsequent inoculations are invaluable
in checking diphtheria. The reason for the presence of diphtheria
to-day is probably because the inoculations are given to school
children instead of children of pre-school age. The susceptibility
to diphtheria is very low at birth, but it increases gradually until
the individual is two or three years old, and then it starts to
decrease. Probably not more than 12 per cent of adults are
susceptible to the disease. Since the Schick test indicates the
individuals who are not immune, preventive treatment, in the
form of toxin- antitoxin, may be given to them.

Diagnosis. The correct diagnosis of diphtheria plays a very
important part in its control. Not only does the safety of the
community depend on the detection and isolation of cases of diph-
theria, but the early recognition of the disease diminishes the
mortality because treatment is also earlier. The only dependable
means of diagnosis is the microscopic examination of cultures
obtained from the throat and nose.

Prevention. Diphtheria has been responsible for the deaths of
so many children that health authorities are trying to prevent the
disease by completely eradicating it. If all school children should
receive the Schick test and be immunized by the toxin-anti-
toxin method, very few diphtheria cases would be found. This
can only be made possible through an educational campaign, by
means of which the people will understand the danger and char-

WH. FITZ. AD. BIO. — 30

458 DIPHTHERIA, SCARLET FEVER, AND TETANUS

acteristics of the disease, and the best methods of controlling
it. If a physician is consulted as soon as suspicious symptoms
appear, he can administer antitoxin immediately and probably
prevent a serious case of the disease. Children should be taught
to keep pencils and all articles handled by other children out
of their mouths. Since diphtheria is a droplet infection, the
same rules for prevention apply here as in other diseases spread
by this means.- Patients who are convalescing from diphtheria
should be kept away from well persons until all danger of spread-
ing the infection is eliminated.

Scarlet Fever

Scarlet fever is a disease similar to diphtheria, in that it works
through toxins. The causative organism has not been definitely
isolated. A chain form of spherical bacteria called streptococci
is always found in the nose and throat of scarlet fever patients,
but there is considerable doubt as to whether this is really the
causative organism. Seventy per cent of the deaths from scarlet
fever are among children under ten years of age.

A test, similar to the Schick test, has recently been prepared
to determine the presence or absence of scarlet fever immunity.
It was devised by two doctors, G. F. and G. H. Dick, and is
called the Dick test It consists of putting small quantities of
toxin prepared from the streptococcus bacillus under the skin of
the child to be tested. There is a reaction similar to that in the
Schick test.

If a child is not immune, subsequent doses of toxin are inocu-
lated. It is not necessary to neutralize the toxin with antitoxin
as in the case of diphtheria, because the scarlet fever toxins are
not as powerful as the diphtheria toxins. This inoculation cre-
ates an active immunity in the child by stimulating its body to
make its own antitoxins. The Dick test and its subsequent in-
oculations are not used to the extent of the Schick test and inoc-

TETANUS

459

illations, but its use seems to be growing constantly. There is
also an antitoxin for scarlet fever. It is prepared from the
horse's blood in a way similar to the preparation of diphtheria
antitoxin. It has been used with considerable success to pro-
duce an immediate immunity in case the child is in the initial
stages of scarlet fever.

The method of transmission of scarlet fever is through droplet
infection similar to that of diphtheria.

Tetanus (Lockjaw)

Tetanus, a disease that develops from the germs entering a
deep injury or wound, is due to the action of the toxins of a par-
ticular microorganism. These toxins affect the brain and spinal
cord. No noticeable effect is produced in the wound through
which the germ enters. Fortunately, tetanus is rare in this coun-
try, but when it does occur *the death rate is very high. The
extensive prevalence of tetanus among the soldiers wounded in the
late World War was ascribed to
the contamination of their wounds
with soil from a highly cultivated
territory which had been regularly
and frequently fertilized with
manure. This soil contained the
germs of the disease.

Cause. This disease is caused
by the tetanus bacillus, a rod-
shaped microorganism which grows
in long, slender threads. These
threads break up.,, into shorter
motile rods surrounded by fla-
gella. These bacilli eventually be-
come non-motile, lose their flagella, and each forms a spore at one
end. This gives to them their characteristic drumstick appear-

Certain bacteria roll themselves up in-
side a thickened wall to form a spore. In
the photomicrograph of the tetanus organ-
isms the spore appears at one end of the
bacillus.

460 DIPHTHERIA, SCARLET FEVER, AND TETANUS

ance. Under favorable conditions these spores remain virulent for
years. The tetanus bacillus was first discovered by Nicolaier in 1884
and cultivated by Kitasato in 1889. Shortly after this, Von Beh-
ring succeeded in producing an effective tetanus antitoxin.

Occurrence. Tetanus bacilli are found in damp soil and in dust,
especially around stables, in manure, and in dust of the house and
street. They are so plentiful in the intestinal contents of horses
and cows, whose wastes are commonly employed to fertilize gar-
dens, that tetanus is sometimes regarded as a disease contracted
indirectly from these animals. Other herbivorous animals also
harbor the germ. The bacilli are likely to be found on rusty nails
or implements which have been in contact with the ground, on
dirty splinters, and* on gunshot.

Tetanus bacilli are anaerobic (cannot grow when exposed to
the air) ; therefore, deep wounds are most favorable for their de-
velopment. They are unusual in that they do not grow on healthy
living tissues, but on cells which have been torn and killed. Badly
lacerated wounds present a more favorable surface for the growth
of tetanus than do those made by very keen clean instruments.

How tetanus enters the body. The bacilli gain entrance to
the body through wounds varying in size from a needle prick to
an operation wound. Being anaerobic, the organisms infect
deep lacerated wounds such as those made on the hand by the
accidental explosion of a toy pistol or wounds on the feet made by
the deep puncture of a rusty nail. Rusty nails themselves never
produce lockjaw, but the bacteria are frequently held in the rough
spots of the rust and consequently enter the body if the nail
happens to puncture the flesh. Occasionally, the disease occurs
without any evident wound. In cases like this, the bacteria have
made an entrance through some unnoticed abrasion of the skin or
the mucous membrane.

Tetanus has been observed not only in man, but in domesticated
animals such as the horse, sheep, dog, cow, and pig.

THE NATURE OF THE DISEASE 461

The nature of the disease. The effects of the disease are due
to the action of toxins produced by the bacilli upon the central
nervous system. The bacilli themselves apparently do not move
from the deep seated area of entrance. The symptoms of tet-
anus are usually noticeable any time from two to nine days
after a wound has been received. The bacillus which entered the
wound as a spore may require some time to become active again.

Treatment. When the organisms have once started to produce
their toxins, hope of controlling the disease is only slight. The
toxins, even though present in the minutest amount, are so very
poisonous to certain parts of the brain and spinal cord that all efforts
to neutralize or counteract the activity are usually of no avail.

Whatever treatment is given must be early. Wounds likely
to be contaminated with tetanus, as those into which soil
may have entered, or gunshot wounds, should be opened and
washed with a strong antiseptic. If the danger of infection is
considerable, the wound should be cauterized. In addition to
this, a dose of tetanus antitoxin (antitetanic serum) ought to be
administered. When precautions have not been taken and " lock-
jaw " sets in, the serum injected into the spinal canal sometimes
brings about the desired result.

Tetanus antitoxin. Certain State Departments of Health pre-
pare antitoxin to be used both in the prevention and in the treat-
ment of the disease. Tetanus bacilli are grown in broth, away
from the air. The resulting liquid, loaded with tetanus toxin, is
filtered gradually and injected at intervals, in increasing amounts,
into the veins of a horse. Later, a large amount of blood is drawn
from the animal and the serum is separated. This serum con-
tains antitoxin which has been produced in the horse to neu-
tralize the introduced toxin. The serum is known as the anti-
tetanic serum. The antitoxin has a high preventative but a low
curative value. Its production is in many ways similar to that
of diphtheria antitoxin.

462 DIPHTHERIA, SCARLET FEVER, AND TETANUS

Prevention. Care should be taken to avoid cuts and wounds of
all kinds, especially from objects soiled with manure or fertilized
soil. The restriction of the use of fireworks during the past few
years has very markedly reduced the number of cases of tetanus
occurring over the country at large. All gunshot and " Fourth
of July " wounds, any extensive or deep wounds, and every form
of punctured wounds should receive care from a physician. Where
such wounds have had dirt driven into them, the desirability of
an injection of tetanus antitoxin is very great. The antitoxin
must be given early as it is preventative and not a cure of
tetanus. Wounds suspected of containing tetanus organisms
should be opened and thoroughly cleaned. Gauze bandages,
which are porous, should be used, never air-tight bandages.

Questions and Suggestions

1. Discuss the discovery of the causative organism of diphtheria.

2. Discuss the work of Emile Roux.

3. Review and report on the work leading to the discovery of
antitoxin.

4. Contrast active and passive immunity.

5. Discuss the Schick test and its importance.

6. How do diphtheria bacilli gain entrance to the body ?

7. How do diphtheria bacilli attack the body ?

8. What educational propaganda for parents is still necessary be-
fore diphtheria can be eradicated ?

9. Contrast and compare scarlet fever with diphtheria in cause,
prevention, and treatment.

10. Explain why the prevention of a disease is more to be desired
than the cure.

11. What is the similarity between tetanus and diphtheria?

12. Where are the tetanus bacilli found ?

13. What is the relation of tetanus to different types of wounds ?

14. Is there any truth in the belief that one will surely get tetanus
if he cuts himself between the thumb and first finger ?

15. Why are tetanus organisms found in dirty places more commonly
than diphtheria or scarlet fever organisms ?

16. What has caused the reduction in the number of deaths from
tetanus ?

QUESTIONS AND SUGGESTIONS 463

17. How should a wound be treated if there is any possibility of
tetanus infection ?

18. Look up and report on the life and work of Loeffler and of
Von Behring.

19. Look up the health bulletin of your village, city, or state and
plot a curve of the number of cases of tetanus reported annually for
the last ten years. Were any of the cases fatal ?

Supplementary Readings

Broadhurst, J., How We Resist Disease (J. B. Lippincott Co.).
De Kruif, P. H., Microbe Hunters (Harcourt, Brace & Co.).
Greaves, J. E. & E. O., Elementary Bacteriology (W. B. Saunders Co.).
Rosenau, M. J., Preventive Medicine and Hygiene (D. Appleton & Co.).

-*•< : ^ .,«. . +-

%*r' ^^ /**%.

CHAPTER XLV
TYPHOID FEVER

Bacterium typhosum

Some have flagella

What is the danger of typhoid infection in the United States f What are
some of the measures of preventing typhoid infection f Why are oysters
a greater source of contamination than milk, in some cities f

Prevalence of typhoid fever. During the Spanish-American
War typhoid spread rapidly through the embarkation camp in
Florida. More men died of fever than were killed in battle.
During the South African War, the British army lost 7582 men
from wounds and 8225 from typhoid. To-day, all soldiers in our
army are required to be vaccinated against typhoid fever; and
typhoid is probably rarer in military camps than in the most
healthful cities and towns. Formerly, the death rate of typhoid
in the United States was forty per 100,000. In the last few years
this number has been reduced to four per 100,000.

Since the World War, the death rate from typhoid has been re-
duced most among men between 29 and 45 years of age. This
is largely due to the education and practice in disease prevention
by vaccination given to the millions of men who were in the army.

Cause. Typhoid is due to a small, motile, rod-shaped bacte-
rium, the typhoid bacillus. It is short, probably about one half
the length of the diphtheria bacillus.

Nature and symptoms of typhoid fever. The disease is located
primarily in the lining of the intestine. The germs then pene-

464

PROTECTION OF THE BODY AGAINST TYPHOID 465

trate the lining and enter the blood stream. The increased ac-
tivity of tissue cells in combating the germs and their toxins causes
fever and the whole body suffers. Convalescence sometimes re-
quires many weeks. Mortality from typhoid fever is about 10 per
cent. From two to four per cent of all persons who have had
typhoid are typhoid carriers for some time after recovery. This
condition may become chronic and remain for years.

One typhoid carrier is reported to have been responsible for
several outbreaks of the disease. He infected 30 persons, 5 of
whom died. Another carrier was a cook who had prepared a large
dish of spaghetti for a dinner. Subsequently, 93 people who
attended the dinner became ill with typhoid. There is a similar
historic case in New York city. " Typhoid Mary " was a cook
and had worked in various families. She had never had the dis-
ease but carried the germs. Fifty cases of typhoid were traced
to her. Since her entire history is not known, she may have
been the cause of many more cases of typhoid. Shie has finally
been confined and her personal habits supervised very carefully to
prevent any further contagion. Because of the danger from car-
riers, the Health Department of various cities and states requires
a thorough physical examination "of all people who handle foods.
This law has resulted in discovering several typhoid carriers and
placing them under strict supervision.

Protection of the body against typhoid. The germs of typhoid
produce powerful endotoxins, toxins within the cell. The body
fortifies itself by producing various protective materials, some
of which dissolve the invading germs and are known as bacteri-
olysin. The body cells also produce chemical substances, called
agglutinins, which cause the germs to be surrounded by a gluelike
substance. This results in a clumping or agglutinating of the once
motile germs of typhoid. When these bacteria are stationary and
in masseS? instead of moving around, the white corpuscles can
more readily devour them. The presence of agglutinins can be

466

TYPHOID FEVER

determined by adding blood of a patient who has typhoid, or
has recently had it, to some typhoid bacilli on a glass slide.

cover- -slip ...Tiangi ng "&rop

? / \ K- o

/ \

' ^ \ ^

'K \ ' ^

; N - v /

The diagram on the left, shows free swimming typhoid bacilli. The one on the right, shows
typhoid bacilli clumped in masses by the presence of agglutinins from the blood of a typhoid pa-
tient. The agglutination test is usually made in a hanging drop on a glass slide as shown above.

When this drop is viewed under the microscope, the germs are
seen clumped together in masses.

One attack of typhoid produces immunity. This is probably due
to the fact that so much protective material is developed to combat
the powerful typhoid toxin that much is left over and stays in the
blood for life. Since the toxin is not an exotoxin as in diph-
theria, antitoxin would be valueless and probably is not produced.
The body combats a disease germ which produces an endotoxin
by fighting the actual germs with their inclosed toxins.

Diagnosis. As early a diagnosis as possible must be made if
the patient is to get the best possible treatment. An early quar-
antine must be established to prevent the spread of the disease
to other people.

METHOD OF SPREAD

467

One method of diagnosis is the examination of cultures, made
from the feces (excreta) of the patient, for the presence of typhoid
germs. Doctors take samples of fecal material from the patient
and send it to the Board of Health laboratories. There the ma-
terial is mixed with media and the developing bacterial colonies
are examined for typhoid bacilli.

Another method of diagnosis is the Widal test. This con-
sists of separating serum from the patient's blood and mixing
it with a culture of known typhoid germs. If the patient has
typhoid, the blood serum will cause the germs to become ag-
glutinated. Agglutinins for typhoid are present in the blood
only when typhoid bacilli are in the body or if a person has
recently recovered from typhoid. The Widal test is a means of
differentiating typhoid fever from other diseases that produce
fever.

Method of Spread. Typhoid germs are spread largely through
materials contaminated by the excreta of typhoid patients. This
may be, and most frequently is, water which has been polluted by
sewage and milk which has
become infected probably
by being kept in containers
which have been washed in
polluted water. Raw foods
such as oysters, if they
are grown where they come
in contact with sewage,
may cause typhoid fever.
Raw foods such as celery
and lettuce, which may
have been watered or
washed with contaminat-
ing water, are frequently carriers of the disease. Insects, princi-
pally the house flies, which travel readily from filth to exposed

•

••

• :

4 ■; 'V ■

■■0 $& :

*?**£;

•*p\* ■•'WB

J***

Agglutinins of various types may be present in the
blood. The picture on the left shows agglutinated
typhoid bacilli, on the right agglutinated pneumonia
cocci.

468 TYPHOID FEVER

foods, are notorious carriers of typhoid germs. Human beings
may also carry and transmit the germs.

Prevention. Typhoid fever can be prevented both by keeping
the typhoid bacilli from entering the body, and by destroying the
bacilli. Since typhoid germs are spread by materials polluted by
human excretions, or by the housefly, or a human carrier, some of
the methods of preventing a typhoid outbreak are the following :

1. Disinfect all excreta of typhoid patients or carriers with
chloride of lime. All clothing and bed linen of a patient should
be disinfected by being boiled or soaked in carbolic acid or bichlo-
ride of mercury solution.

2. Provide a good sewage system.

3. Provide a good water supply. Chlorinate the water. (Boil
the water if an infection is suspected.)

4. Pasteurize all milk, or require such sanitary milking condi-
tions that pasteurization is unnecessary. Following the introduc-
tion of pasteurization of milk in several cities in 1914, there was a
marked decrease in typhoid.

5. There should be proper handling of foods in the grocery, in the
market, and in the home. Food should be properly covered and
protected from flies. Foods which have been exposed should be
thoroughly washed.

6. Health certificates should be required from persons who
handle foods in order to eliminate the danger of typhoid carriers.

7. There should be a proper control of the house fly. The de-
struction of their breeding places, keeping the premises clean and
garbage covered, screening the houses, and screening the sick-
rooms will help exterminate the house fly.

8. Vacationists, nurses, doctors, and any other people who are
likely to be exposed to typhoid infection or unsanitary conditions,
should be vaccinated. People may be immunized at any clinic,
providing they cannot afford to have their own doctors immunize
them. The immunity usually lasts from two to four years.

VACCINATION

469

Vaccination. Immunity to typhoid may be gained artificially
through vaccination. In the case of smallpox vaccine, the germ
material was weakened through cultivating it in animals. In
preparing typhoid vaccine, the bacilli are first grown on agar,
then killed by heat, and a little carbolic -acid is added to the vac-
cine for a preservative. When this material is used as a vaccine,
the presence of the dead bacilli stimulates the body to make bac-
teriolysins and agglutinins. Thus a vaccinated person is pro-
tected against the invasion of living germs. Usually three
inoculations of vaccine are given, each being seven days apart.

Very few people are made ill by typhoid vaccination. If the
person is likely to come in contact with paratyphoid, which is a
disease somewhat similar to typhoid,
he is given a combination vaccine of
typhoid and paratyphoid. For most
people living in the United States
or visiting here, the typhoid vaccine
is sufficient, because there are few
cases of paratyphoid in the United
States.

The investigation of a typical epi-
demic. During November, 1924, there
was a noticeable rise in the number
of typhoid fever cases in New York
city. This continued through January,
1925. Of the 914 cases recorded in
this outbreak, 116 of the residents, and
59 nonresidents who were included
in the 914 cases, gave a history of
having been out-of-town during the
period immediately before their illness.
The majority of these had eaten oysters while out-of-town. About
18 per cent of the cases probably acquired their infections in

//«*

^?K

At &

?/3r ■■-*%

/ V

% ' ,♦ %%*\

,* VR <5W

f* * "V'J

I * >

<* <► ' * % *j

V <

?r ?f& i 7

Y A*.

v % y*s+y-

t« w

* ■ ><.■. ,

uj*~ *±sf

Bacterium coli.

These organisms are commonly
present in the intestine of man.
Their presence in swimming pools
indicates the possibility of contami-
nation by human excreta. This
might also indicate the possible
presence of typhoid bacilli. Bac-
teriological examinations of water
in swimming pools are frequently
made to determine the presence of
bacterium coli. Their presence
would make the closing of the pool
imperative until proper prophylactic
measures were taken.

470

TYPHOID FEVER

this way, but that did not explain the cause of the other cases, so

the investigation continued.
The water supply of most cities is constantly tested for bacillus

coli, a microorganism found in all human intestines. If the

bacilli coli are
present, there is
the likelihood of
typhoid also being
present. The
water of many
cities is chlorinated
and this results in
purification. The

1961

967

civil. Spanish - World

SVAR AMEQfCAN WaQ,

A surgeon general of the U. S. Army has compared the death bacilli Coli are
rates of men treated in hospitals for typhoid, during the first two . ■. ,

years of three different wars. The diagram indicates the number practically never

of deaths in every iO.000 cases. ^^ ^ ^^

which is thoroughly chlorinated. Since the water supply was
chlorinated, it could not have been responsible for this epidemic.

The milk supply was investigated and nothing definite was
found. The investigators paid particular attention to milk,
because in 1913, before pasteurization, an infected milk supply was
responsible for 521 cases and 61 deaths from typhoid. Ice
cream, water ices, and bottled water supplies were investigated.
Again there was no evidence of infection. Uncooked foods, par-
ticularly lettuce and celery, were scrutinized with care. No
worthwhile evidence was revealed there..

The first bit of evidence was that a great number of the re-
maining cases gave a history of having eaten oysters approxi-
mately two weeks before the onset of the symptoms. Fifty-five
per cent or 506 cases gave a definite history of having eaten
oysters. In April, 1915, a similar condition had existed. In an
outbreak of 150 cases, 80 per cent seemed to be due to the use
of raw oysters. Even when oysters are grown in clean, unin-

THE INVESTIGATION OF A TYPICAL EPIDEMIC 471

fected water, they are frequently contaminated by the people
who gather, ship, or otherwise handle them. The same safe-
guards which have been established to protect milk from pollu-
tion at each and every stage of its handling must be exercised
in the handling of oysters.

A number of the remedies have been suggested in order to pre-
vent similar epidemics of typhoid fever. The shores and water
that have been set apart for oyster beds should be constantly
guarded and examined. Sewage and the contents of cesspools
should not be emptied near them. Boats, both pleasure and Com-
mercial, should be prohibited in such districts. Oysters from a
polluted stream should not be transplanted. The gathering, pack-
ing and shipping of all shellfish should be efficiently supervised,
and the people who handle them in any way should receive fre-
quent and thorough examinations.

In the summer of 1928, tests were made of the waters of vari-
ous bathing beaches near different cities and in many cases the
water was found to be polluted. The Commissioners of Health
suggested that bathing be prohibited in these places. This was
not done as certain authorities claimed that the value of the sun-
shine and bathing was so great, and that it was so possible and

In New York city there has been a steady decrease of deaths from typhoid fever since pas-
teurization of milk has been required.

472 TYPHOID FEVER

easy to secure immunity from typhoid fever by vaccination, that
all bathers should be immunized and thus be protected. Many
followed this suggestion. It is always advisable for bathers usin&
water that may become contaminated to be vaccinated. In this
way such recreation will be healthful as Well as pleasurable.

Questions and Suggestions

1. Compare typhoid fever statistics in the Spanish- American
War and the World War.

2. Discuss the dangers of typhoid carriers fo a community.

3. Name two antibodies produced by the body as protection
against typhoid. Discuss the importance of each.

4. Discuss the relation of white corpuscles to combating typhoid
in the body.

5. What is the value of an early diagnosis of typhoid fever ?

6. Describe two methods used in accurately diagnosing typhoid.

7. How is typhoid fever spread ? How can it be prevented ?

8. Explain the preparation and use of typhoid vaccine.

9. Discuss how an investigation of a typhoid epidemic is carried on.

10. Why is it unwise to drink water from springs within city limits ?

11. Why is the water of swimming pools constantly tested ? What
does the presence of bacilli coli indicate ?

12. Why is it more important for a traveler to have typhoid vac-
cination than for one staying at home ?

13. Discuss any epidemic of typhoid that has been in your home
town or city.

Supplementary Readings

Broadhurst, J., How We Resist Disease (J. B. Lippincott Co.).
Dublin, L. I., Health and Wealth (Harper & Bros.).
Meredith, F. L., Hygiene (P. Blakiston's Son & Co.).

CHAPTER XLVI

^Hf* - Jf:\ ft '"

CERTAIN OTHER

A ' ,

BACTERIA

fP^

Fleas may carry bubonic
plague.

The louse may carry typhus
fever.

i/ow mai/ co/ds 6e prevented f Have colds any serious effects on the
body? Is there any relation of asthma to food? Is it possible or
desirable for children to avoid the so-called children's diseases ?

Causes of colds. It is generally conceded that there are two
types of inflammation called colds. The first type is caused by
bacteria and is a real infection. The germs may attack a certain
local area, thus causing a cold in the head, a sore throat, laryngi-
tis, or tonsillitis, or they may have general widespread effects as
in grippe. The second type of cold is caused by physical agents
such as irritant gases or dust. Colds and even pneumonia have
been caused by breathing in talcum powder. Dust inhaled in
working at trades such as diamond polishing, metal polishing, or
marble quarrying may cause colds, followed by pneumonia, or
tuberculosis. It is the physical material which starts the irrita-
tion, then bacteria enter the irritated tissues and set up infections.
Other factors that may cause colds are dry heated air, drafts,
sudden changes of temperature, exposure to cold and wet, im-
proper food, and constipation.

Effect of colds on the body. Bacteria causing colds are usually
present in the mucous membrane of the nose, mouth, and throat.
When the resistance of the body is lowered, it is thought that

WH. FITZ. AD. BIO. — 31

473

474 CERTAIN OTHER BACTERIA

these bacteria gain a foothold and produce the condition known as
a cold. Blood congests in the mucous membrane which becomes
swollen and causes a profuse flow of mucus. The mucous mem-
brane of the tear ducts may also swell and the tears will flow con-
tinuously. If the inflammation spreads to the Eustachian tubes,
they may become closed and hearing is temporarily impaired. If
the infection extends to the middle ear, earache usually results.
Sometimes infection may extend to the cavities in the bones of
the front of the skull called the sinuses and cause inflammation
or sinusitis. If the infected material is retained in the sinus, the
condition usually becomes chronic.

A chronic cold is known as catarrh. If the disease extends
down into the bronchial tubes, the condition is known as bron-
chitis ; the inflammation of the finer bronchi may cause broncho-
pneumonia. People who work indoors and at sedentary occupa-
tions are more likely to suffer from colds than persons who live an
outdoor life, as dust, dry air, and noxious gases are continually
irritating the respiratory tract and making it susceptible to infec-
tion. These same predisposing factors increase the likelihood of
the disease extending into broncho-pneumonia. This type of pneu-
monia is unlike lobar pneumonia. The latter is caused by a specific
microorganism, the pneumococcus. Broncho-pneumonia may be
caused by any bacteria that infect the bronchial tubes and air
sacs.

Colds are frequently neglected and considered of trivial im-
portance. Each cold lowers the resistance and vitality of the
body to such an extent that the sufferer is likely to contract other
infections. This may hasten the progress of a serious disease like
tuberculosis. Every effort should be made to prevent colds. Once
a cold is contracted, the best possible care should be taken to
avoid any secondary infections.

Method of spread. Even with many of the predisposing fac-
tors present, a cold does not develop unless there is an exposure

PREVENTION OF COLDS 475

to infection from another person who has or is just recovering
from a cold. Sometimes the infection already exists in the indi-
vidual in a chronic but extremely mild state, and it may become
acute when the vitality or resistance is lowered. Eskimos and
Arctic explorers, in spite of the severe weather conditions, do not
have colds. When such explorers return to civilization they may
be infected by droplets sprayed by the coughing and sneezing of
people whom they meet, and they soon experience a severe cold.

Prevention of colds. Since a cold is a droplet infection, it
generally travels through the sputum. Crowds in ill ventilated
places should be avoided. The germs can live only for a very short
time in air. Their culture medium is the air passages of human
beings. In crowds, it is impossible to avoid the sneezing or
coughing of other people. That is the way colds are spread and it
is the reason for the frequency of colds. Spitting spreads sputum-
laden bacteria into the air. If a person talks directly into the face
of another person, droplets of sputum are given off and inhaled.

An experiment was made in England to show that droplets
from the mouth are spread. A certain member of Parliament was
asked to wash out his mouth with a culture of harmless bacteria
which, when plated, produce red colonies. He then made a loud
and eloquent speech. Petri dishes had been distributed in all
parts of the House of Parliament, even to the rear of the gallery.
When gathered, incubated, and the plates examined, all the ex-
posed dishes contained red colonies. The closed controls showed
none. The speaker had showered the entire house with micro-
scopic droplets containing the harmless bacteria.

Coughs and sneezes must be covered in order to prevent the
spread of infections. When a person has a cold, he should use
gauze instead of handkerchiefs and the used gauze should be burned.
Some people seem to be more susceptible to colds than others.
This may be due to abnormalities in the nose or throat. Ade-
noids and infected or enlarged tonsils are excellent locations for

476 CERTAIN OTHER BACTERIA

the harboring and growth of germs, and should be removed.
Teeth should be straightened so that correct breathing will be
possible. Nasal douches should not be used regularly, as the
solutions used in them may be irritating to the delicate mucous
membranes, and may cause an infection. If the nasal passages
are in healthy condition, strict observance of the rules of individ-
ual hygiene is likely to prevent colds. Living and sleeping out-
of-doors will keep fresh air in the lungs and will prevent colds.
Children with colds should be kept home from school in order to
keep the infection from spreading.

Remedial measures. A cold is very likely to run a regular
course, although proper treatment may relieve some of its un-
pleasant features. The patient should avoid drafts and keep warm.
If it is possible to stay in bed for a day, many of the symptoms
can be mitigated. A hot foot-bath, hot drink, and massaging
the neck and chest well just before going to bed are often very
beneficial. These measures help in stimulating circulation and in
breaking up the congestion. If the weather is mild and sunny,
the patient should spend as much time as possible out-of-doors.
There are special vaccines prepared against colds and used with
some slight degree of success. They are sometimes successful in
stimulating a person's body to work up an immunity.

Influenza. Epidemics of influenza have spread all over the
world, therefore, it is frequently called a pandemic disease. In-
fluenza of the respiratory tract is the most common form of the
disease, although there are other forms. It usually starts with a
cold, followed by a high temperature and extreme weakness. It
may extend into the lungs and cause bronchitis or pneumonia.
The disease is spread by direct contact. The secretions of the
mouth and nose carry the infectious agents. Droplet infection
is generally considered to be the method of spreading influenza.
Unlike many other diseases, one attack does not usually establish
an immunity.

ASTHMA

477

Asthma. Any condition of difficulty in breathing is popularly
known as asthma. Some conditions of asthma are due to lung
infections, others to food poisoning. If cer-
tain foods disagree with a person, the reaction
may be shown by an asthmatic condition.
Frequently, rashes are caused by a sensi-
tivity to certain foods. In order to discover
what food is causing the reaction, different
foods are injected below the skin. If the skin
shows irritation, the food causing it is taken
from the diet and the asthma often clears up.

When a plant pollen causes asthma, it is
known as hay fever. Vaccinations of pollen
are inoculated into the skin to see which of
the pollens cause the sensitivity. The pollen
from the ragweed is responsible for many cases
of hay fever. When the right pollen is de-
termined, small quantities of it are inoculated
into the sensitive person until he works up
an immunity. Up to the present time these
vaccinations have not always proved suc-
cessful.

Focal infections. Bacteria at some point
or focus in the body frequently, multiply and
produce toxins which are absorbed into the
body and affect other parts. When people
tire easily, lack normal energy, and are
subject to pains in the joints and muscles,
they may have a focal infection. Other
evidences of focal infections are inflammatory
rheumatism, heart disease, kidney disease, lumbago, and nervous
conditions such as neuritis and neuralgia. 'When any of these
conditions occurs, the doctor usually looks for a focal infection.

Skin tests may be made
to determine an individ-
ual's sensitivity to differ-
ent foods. Small volumes
of different foods are in-
jected under the skin or
small amounts are rubbed
into tiny gashes made on
the arm. One cut, the
control, is not treated with
food. Little or no red-
ness or soreness is pres-
ent near the control.
Varying amounts of in-
flammation appear about
the infected areas. Red-
ness and soreness denote
a positive reaction and
indicate sensitivity.

478 CERTAIN OTHER BACTERIA

Common foci of infection in the body are diseased tonsils,
chronic infections of the ear and nasal cavities, which may spread
to the sinuses, pockets of pus about the roots of the teeth, and a
diseased appendix. When the focus of infection is removed, the
symptoms tend to disappear. Regular and systematic care of
the teeth by a competent dentist, with the use of X-rays when-
ever possible, will bring to light pus pockets in teeth. Avoidance
of, and proper care of colds will prevent sinus and ear infections.
Regular periodic health examinations will usually detect these
foci of pus before they cause disease in the body. Once a focal
infection is started, it may be very difficult to cure it.

Measles, whooping cough, and chicken pox. These diseases
are common among children because they are spread through the
unhygienic habits that are prevalent among all children. When
a little girl hugs another one, takes a bite of her apple, borrows her
pencil, or performs endless other acts that result in personal con-
tact, disease germs may be passed from one child to the other.
In some households, if one child contracts one of these diseases,
all the children of the family are purposely exposed to it. It is
easier to take care of all at the same time. This is a very wrong
procedure. These diseases, in themselves, are not very serious
and seldom fatal. But they are frequently followed by secondary
infections such as pneumonia, deafness, rheumatism, heart disease,
or kidney disease. The after-effects are far more serious than
the original disease. When one child gets a disease from an-
other, the second child may get it in a more severe form than the
first. In growing in the first child's body, the disease germ seems
to acquire greater virulence and, consequently, affects the second
child more seriously. Either this is the case or weaker strains of
bacteria are killed in the first child's body and only those virulent
organisms that are resistant to the defenses of the child's body are
passed on. Children who show any signs of illness should remain
home from school until they are again perfectly well. Because

QUESTIONS AND SUGGESTIONS 479

they can stay out in the sunny open air, if well enough, or relax
in bed, their recovery will be hastened, and they will not spread the
infection through the school.

Questions and Suggestions

1. Discuss the causes of different kinds of colds.

2. What effects have colds on the body ?

3. How are colds spread ?

4. How can the vitality of the body be kept high so that colds may
be prevented ?

5. What unhygienic practices have you noticed among students
which may account for epidemics of colds in a school ?

6. How can epidemics of colds in schools be prevented ?

7. Compare influenza to an ordinary cold.

8. Discuss the common causes of asthma.

9. What do asthma vaccinations consist of?

10. Discuss focal infections and their relation to the health of the
body.

11. What is the relation of so-called children's diseases to the vital-
ity of a child ?

12. Discuss some after-effects that may result from measles,
whooping cough, and chicken pox.

Supplementary Readings

Broadhurst, How We Resist Disease (J. B. Lippincott Co.).
Haggard, H. W., The Science of Health and Disease (Harper & Bros.).
Rosenau, M. J., Preventive Medicine and Hygiene (D. Appleton & Co.).

CHAPTER XLVII

THE CONTROL OF

MALARIA AND

YELLOW FEVER

Walter Reed.

Underwood & Underwood
Hideyo Noguchi.

How has malaria been controlled? Why ivere the French unable to
build the Panama Canal f Who was Hideyo Noguchi?

Malaria is caused by a microscopic protozoan, known as a
Plasmodium. There is some discussion as to whether the organism
that produces yellow fever has really been isolated.

Prevalence of malaria. In 1908 there were more than three
million deaths from malaria in India. Along the rivers and
coasts of tropical countries, malaria is the white man's greatest
obstacle to settlement. In temperate climates such as the
L T nited States malaria is not usually fatal, but in the tropical
countries it occurs in most severe forms and the death rate is
very high.

The use of the drug, quinine, is most effective in treating malaria,
since it kills the malaria protozoans in the blood. In 1902, the
Italian government began the sale of quinine at low prices to
certain communities. This drug was distributed free to those
unable to purchase it. In 1904, the Italian towns gave it to all
working people. In consequence, there has been a progressive
reduction in the amount of malaria in Italy. During the ten
years previous to 1902, Italy averaged 14,048 deaths per year from
malaria. In the nine years following 1902, the average fell to 3853.

4<so

HISTORY OF MALARIA

481

Fifty years ago malaria was so common in our Middle Western
States that it was a serious problem. But this malady has grad-
ually been reduced by scientific control.

Malaria is still fairly common in the tropical countries. It
was recently estimated that, approximately, 90 per cent of the
people of Calcutta are suffering from this disease.

History of malaria. The ancient Greeks thought that malaria
was due to bad air arising from the marshes. Hence they called
the disease malaria, which means bad air. Malaria always pre-
vailed near swamps and was thought to be caused by some kind
of emanation from decaying matter. In 1880, a French army
surgeon, Charles Laveran, noted and described the malarial para-
sites in the red corpuscles of the blood of persons suffering from
malaria. But he was not able to ascertain how they entered the
blood. This was not learned until 1895, by Major Ronald Ross,
an English army surgeon, who started investigating malaria in
India, where malaria was prevalent and existed in its worst form.
Discovering that birds were
susceptible to malaria, he
first studied the organisms in
the blood of the birds. He
suspected that this disease
was not contagious but was
transmitted by the bite of a
mosquito, and he permitted
mosquitoes of a certain spe-
cies to bite infected birds.
He killed the mosquitoes,
and found little swellings in
the walls of their stomachs.
Then he let similar mosqui-
toes bite birds that were not infected with malaria, and no such
swellings appeared in the stomach walls. He continued examin-

10RTALITY PER
1 ' 1 TROM

g ;

WOO POPOLATIOfi
000 TO 01
.01 • OS

as ■ io

10 - 20

to ■ «o

40 - 60
60 • .80
. 00 ■ 2.00

eoo • 3.oo

' \ * \r*2

S~^

£^

»\

**§

1900

1908

"Mbr-taUty from >Talaria in ttakr

Am. Museum of Nat. Hist.
The Italian government has steadily decreased
the cases and deaths from malaria.

482 THE CONTROL OF MALARIA AND YELLOW FEVER

ing many of these small swellings in the stomach of the mosquitoes
and found that they contained numerous parasites. When the
swellings reached a certain size they would burst and the parasites
were scattered through the mosquito's body. Some entered the
salivary glands. Ross concluded that these parasites in the saliva
of the mosquito would pass into the blood of the bird when the
mosquito bit the bird.

Cause. Malaria is caused by a protozoan parasite, Plasmodium
malariae, somewhat like the amoeba. It has two hosts : the
female mosquito of the genus Anopheles, and man. There are
really three different types of malaria, caused by three different
but related microorganisms. Malaria occurring in our latitude is
a mild form of the disease.

Spread. The germ of the disease is spread by the bite of the
female Anopheles which has previously bitten a malarial patient.
(The male feeds on plant juices.) The common mosquito,
of the genus Culex, does not transmit malaria or yellow fever.

Life history of the malaria parasite, Plasmodium malariae. The
amoeba-like organism of malaria cannot complete its life history
in the blood stream of man alone ; it requires two hosts, the mos-
quito and man. Germs are injected into man through the bite of
an infected mosquito. They enter the red blood corpuscles and
multiply there, finally forming from six to sixteen spores. At inter-
vals of 24, 48, or 72 hours, depending on the type of malaria, the
spores, having destroyed the corpuscle, escape into the blood
stream. The sudden release of these poisons, and the subsequent
rallying of the body in an effort to counteract them, are thought
to cause the chills and then the fever which are characteristic of
malaria.

Each escaped parasite now fastens itself to another red cor-
puscle, enlarges, forms spores, and having used up and disinte-
grated the corpuscle, again is set free, not as one but as many
parasites. The cycle is repeated over and over again, until the

LIFE HISTORY OF THE MALARIA PARASITE 483

patient recovers or succumbs. Some of the parasites undergo
certain changes which differentiate them into sex cells. Since all
the parasites were injected into the blood at approximately the
same time, and since it takes each one just so long to grow, form
spores, excrete wastes, and escape from the corpuscle, all, with
their wastes, are ejected into the blood stream at one time.
Therefore, the chills and fever occur at intermittent periods.

When a mosquito bites a patient, it takes in the malarial
patient's blood with the plasmodia which developed into two
types of sex cells. These undergo divisions and changes. Study
the diagram (p. 484) and note that some cells take different forms.
Some of them become male cells, others, female cells. Fertiliza-

etxle^c moscjvcito

anopheles moscjuitd

Culex, the house mosquito, differs in appearance from Anopheles, the malarial mosquito.
Compare the different stages of growth in the life of these two insects.

tion occurs in the stomach of the mosquito by the union of the
male and female plasmodia. The fertilized cells bore into the

484 THE CONTROL OF MALARIA AND YELLOW FEVER

wall of the stomach and form cysts on the outer stomach wall. In
these cysts, the parasites break into thousands of needle-shaped

spores, which finally
escape from the cysts,
enter the blood of the
mosquito, make their
way around the body,
and especially infect
the salivary glands.
When the mosquito
now bites another per-
son, malarial organ-
isms enter the victim's
body with the mos-
quito's saliva. The
malarial parasite
seems to produce no
ill effects on the mos-
quito. In the human
host the malarial para-
site reproduces asexu-
ally and differentiates
into sex cells which
may be called a sexual
phase ; in the body of

The malarial parasite undergoes a cycle in its life history ±U~ mn«srmi+n it ror»rn

from mosquito to man and back again to the mosquito. U1C 111US 4 U1LU 1L ii^wn

Trace the complete history of the organism in the diagram duces both SeXUallv
above.

and asexually.
Nature. The poison produced by the germs causes a marked
chill, followed by fever, then profuse perspiration, and a fall of
temperature. This is followed by a period of well-being until the
onset of the next chill, usually 48 hours later in our type of
malarias Destruction of the red corpuscles may cause anaemia

DIAGNOSIS OF MALARIA

485

and general weakness, which is particularly serious in that it often
renders the body more susceptible to the attack of other diseases.
Common malaria is rarely fatal, but it does weaken the body's
resistance. . Tropical malaria is often fatal.

Diagnosis. The presence of malarial parasites may be ascer-
tained by a microscopic examination of a blood sample. Chills,
followed by fever often come with other, diseases such as typhoid
and appendicitis, which are sometimes diagnosed as malaria. A
microscopic examination gives a conclusive test for malaria as the
Plasmodia will be found' present in the suspect's blood.

Treatment. Frequent doses of quinine bring about the de-
struction of the malarial parasite, but because of the peculiar effect

Photomicrograph of a mosquito's head.

The female Anopheles is the carrier of the malarial germ. The male does

not feed on human blood.

of quinine on the nerves of the ears, and on the salivary glands, it
must be used with care and discretion.

486 THE CONTROL OF MALARIA AND YELLOW FEVER

Prevention. The control
of malaria depends upon the
destruction of malaria germs
in patients by the use of qui-
nine and the destruction of
the mosquitoes (Anopheles).
The frequent use of quinine
in malarial regions by those
not sick will kill the parasite
before it has a chance to
multiply. The rooms oc-
cupied by malarial patients
should be thoroughly
screened, so that the disease
may not be spread through
the infection of more mos-
quitoes. In fact, all dwell-
ings in any malarial district
should be well screened. Since the mosquitoes are in search
of food in the evening, it is unwise for people to go beyond
screen protection after dusk. Probably the best method of eradi-
cating malaria is to destroy the breeding places of the mosquitoes
by draining the swamps and filling in the low places.

Photomicrograph of malarial parasites in a red
blood corpuscle.

Yellow Fever

Prevalence of yellow fever. Yellow fever is a much more severe
disease than malaria. The mortality in various epidemics has
ranged from 15 per cent to 85 per cent of the population. It is
also a disease which is more prevalent in tropical and subtropical
countries than in cooler climates. Formerly, epidemics occurred
in the Southern States, and the disease was very common in Cuba
and the Canal Zone. Much has been accomplished in the last
thirty years in eradicating this disease. In 1878, there were one

HISTORY OF THE CONTROL OF YELLOW FEVER 487

hundred and twenty-five thousand cases and twelve deaths from
yellow fever in the United States. Since 1905 not a single case
has been reported. Havana and Rio de Janeiro used to b(Tcen-
ters of infection. To-day, due to the control of yellow fever, they
are health and vacation resorts. There is still one very bad dis-
trict in western Africa. Efforts are now being made to control
the fever there.

History of the control of yellow fever. It is claimed that yellow
fever was the disease that nearly annihilated the second expedi-
tion of Columbus in Santo Domingo in 1495.

Yellow fever was so bad in certain parts of Cuba that no one
could live there safely. In 1900, after the Spanish-American
War, a commission was appointed to make an investigation of
yellow fever in Havana. The
commission was composed of
Major Walter Reed, a bacteriol-
ogist, and Dr. James Carroll,
Dr. Jesse W. Lazear, and Dr.
Aristides Agramonte. Dr. Reed
could not find a microorganism in
the blood of the infected people.
He decided that if the fever
were caused by a bacterium, the
nurses handling the patients
would contract the disease. This
did not seem to be true. He also
observed that members of the
same family did not seem to get
the disease from each other.
At the end of two or three
weeks, people in the neighbor-
hood of the original cases would

Contract the disease. This Photomicrograph of a mosquito larva.

488 THE CONTROL OF MALARIA AND YELLOW FEVER

seemed to indicate that the germ was transmitted by a carrier,
possibly an insect, and it took that length of time to grow in the

Am. Museum of Nat. Hist.
The numerous swamps of Havana were the breeding places for mosquitoes, and yellow
fever was very prevalent. By 1900, the effect of the extermination of mosquitoes began to be
evident in a lower death rate of yellow fever.

insect's body. Probably the knowledge of the cause of malaria
gave these investigators clues on which they based these theories.

People had formerly thought that yellow fever was transmitted
by fomites, substances such as garments and bedding, which had
been in contact with yellow fever patients and had absorbed the
germs. To test the fomes theory, an experimental hut was
filled with articles from a hospital for yellow fever, at Havana.
Volunteers agreed to sleep in this hut. They did not contract
the disease. The experiment was repeated with a number of
persons and always with the same results, which definitely proved
that fomites did not transmit the disease.

The theory that the disease was transmitted by mosquitoes

HISTORY OF THE CONTROL OP YELLOW FEVER 489

was then investigated. No animal was susceptible to yellow
fever, so Major Reed could not experiment on animals. Dr.
Carroll permitted himself to be bitten by a mosquito known as
the Aedes or Stegomyia mosquito which was suspected of trans-
mitting the fever. He contracted yellow fever but recovered.
A mosquito accidentally alighted on Dr. Lazear's hand and he
permitted it to bite him. He died September 25, 1900, one of
the first martyrs to the yellow fever investigation.

Major Reed then decided to set up controlled experiments to
prove definitely whether or not the mosquito carried the disease.
He wanted to segregate a group of men for a number of weeks
from all contact with yellow fever to make sure they had not
already contracted it before mosquitoes bit them. He asked fcr

(800

1600
1400

' Deaths in
tt avarice
from i
TTakrria ]

1000

800

€00

400

200

JL-

o 1 M Sfli&'v^lk

1675 ifteoiees iseo i$9s two taos u»»

Am. Museum of Nat. Hist.
Due to the control of the mosquito, malaria has practically disappeared from Harana.

volunteers for the experiment. Private Kissinger of Ohio and
John J. Moran, a civilian clerk, offered themselves. Major Reed

WH. FITZ. AD. BIO. — 32

490 THE CONTROL OF MALARIA AND YELLOW FEVER

carefully explained the dangers of the experiment. The volun-
teers said they understood the ravages of the disease but "we
volunteer solely for the cause of humanity and in the interest of
science." They'asked for no compensation for their services. It
was a tense, dramatic moment when the Major raised his hand in
salute to the private, saying, "Gentlemen, I salute you!" His
further comment was, " In my opinion this exhibition of moral
courage has never been surpassed in the annals of the army of the
United States." Kissinger and Moran were bitten by mosquitoes.
They both contracted yellow fever but both recovered. After
studying many other cases, the investigators concluded that
the only way to contract yellow fever is through the bite of an
infected mosquito. It takes about twelve days for the parasite
to complete its cycle in the mosquito's body. Therefore, an in-
fected mosquito does not transmit the disease until about twelve
days after 'taking in the -parasite from the body of an infected
person. *

Am. Museum o/Alat. Hist.
Camp Lazear, Cuba, was the experimental camp in which the yellow fever investigation was
conducted. It was named for Dr. Jesse W. Lazear, who died a martyr to the investigation.

For 130 years Havana had been continuously infested with yel-
low fever. The average death rate from it was about 750 deaths

HISTORY OF THE CONTROL OF YELLOW FEVER 491

per year. After the yellow fever investigation, Major Gorgas
was sent by the United States government to rid Havana of mos-
quitoes. Within ninety
days there was not a single
new case of yellow fever.

The Isthmus of Panama
was considered a plague
spot for yellow fever and
malaria. About 1880, the
French started building a
canal across the Isthmus,
but had to give it up, be-
cause of the prevalence of
the diseases which caused
the death of thousands
of the workers. Twenty
years later, the United
States bought the Isthmus
from the French. Since
Gorgas had helped to rid
Havana of yellow fever,
the government sent him
to eradicate yellow fever
from Panama. There were
neither suitable drains nor water supply in the cities, so Gorgas
had a system of drainage constructed, the streets paved to elimi-
nate water-filled ruts, the water supply of the cities improved, and
the windows and doors screened against mosquitoes. Pools were
either drained or oiled. Endless care, thought, and time were
devoted to this work. In about two years yellow fever was
eradicated from the Isthmus and the building of the canal was
made possible. This was as great a hygienic feat as the canal
was an engineering feat.

Courtesy Rockefeller Institute
The structure isolated by Dr. Nogucbi which is
believed to be the cause of yellow fever. In the photo,
the spirochaete is magnified 3000 times.

492 THE CONTROL OF MALARIA AND YELLOW FEVER

Later Investigations. Hideyo Noguchi of the Rockefeller Insti-
tute isolated a microorganism, called a spirochaete, from yellow
fever victims in South America, which has been, until recently, a
focus for yellow fever. It is more like a protozoan than a bac-
terium. He made a vaccine from this organism, which is admin-
istered early in the disease and is very effective. The disease
has been practically exterminated in the Western Hemisphere,
due to his efforts. But experimental workers in Africa were
unable to isolate the spirochaete from the blood of victims of
yellow fever in that country. They were unable to inoculate
monkeys and guinea pigs with the disease as Noguchi had done.
Apparently, the germ causing yellow fever in Africa was differ-
ent from that causing the disease in South America. Noguchi
went to Africa to investigate the disease and he succeeded in
inoculating one species of monkey with the disease. Unfortu-
nately Noguchi became infected with yellow fever in Lagos,
Nigeria, and died in the spring of 1928. After he contracted
the fever, he insisted that samples of his own blood be inoculated
into monkeys. His associates carried on his experiments with
the cultures which he had started. It has not yet been decided
whether there are one or two types of yellow fever. From data
left by Noguchi, the Rockefeller Institute for Medical Research
is inclined to believe that there are two distinct forms of the
disease. Scientists are most anxious to clear up the infection
in western Africa before the transcontinental railroad is opened.
If the disease spreads to the East Coast, it may pass over into
India and southern China, which are full of the Aedes mosquito.

Cause. A spiral protozoan, spirochaete, was discovered in
1918 by Noguchi and designated by him as the cause of yellow
fever. Experiments are being performed, at the present time, to
determine whether or not the spirochaete is really the specific or-
ganism causing yellow fever. The vaccine prepared by Noguchi
has not yet been accepted as a definite preventive.

QUESTIONS AND SUGGESTIONS 493

Questions and Suggestions

1. Discuss the prevalence of malaria in the world.

2. How did the disease receive its name ?

3. Discuss the experiments of Major Ross.

4. Discuss the cause and spread of malaria.

5. Discuss the life history of the malarial parasite, including
both the asexual and sexual phases.

6. What effect has malaria on the body ?

- 7. How is malaria diagnosed ; how is it prevented ?

8. Discuss the prevalence of yellow fever.

9. Discuss the investigation conducted by Major Reed.

10. What biological and sociological effects did the investigation of
yellow fever have on Havana ?

11. Why is the building of the Panama Canal considered as great
a hygienic as an engineering feat ?

12. Discuss the contribution of Hideyo Noguchi to the eradication
of yellow fever.

13. Discuss the cause and the method of spread of yellow fever.

14. Discuss the prevention of yellow fever.

15. Which of Koch's postulates was Noguchi unable to carry out
in his investigation of yellow fever ?

16. Does the government give pensions or aid in any form to per-
sons (or their dependents) who have risked their lives in scientific
investigations ?

Supplementary Readings^

De Kruif, P., Microbe Hunters (Harcourt, Brace & Co.).
Greaves, J. E. & E. O., Elementary Bacteriology (W. B. Saunders Co.).
Haggard, H. W., The Science of Health and Disease (Harper & Bros.).
Zinsser, Hans, A Textbook of Bacteriology (D. Appleton & Co.).

Ifw^f

CHAPTER XLVIII

DEFENSES
AGAINST DISEASE

The scavengers of the body.

Antitoxins neutralize toxins.

How is the body protected against bacteria? Are the protections
adequate? Under what conditions are the defenses inadequate?

Diseases of the body may be due to glandular disturbances
such as cretinism; inadequate diets, as rickets; constitutional
tendencies or disturbances ; or to infections from microorganisms.
Parasitic microorganisms exist in great numbers, but most of
them are either kept out of the body or destroyed when they enter
the body. There are comparatively few diseases caused by bac-
teria when compared with the existing number of parasitic
bacteria.

Behavior of bacteria in the body. Bacteria have different
modes of attack and different ways of breaking through the de-
fenses of the body. Some bacteria actually destroy tissue. For
example, the tuberculosis bacillus devours various tissue cells,
and thus destroys them. It is thought that certain parasitic bac-
teria which cause boils and abscesses send out enzymes which
dissolve the white blood cells so that they can be absorbed by
the bacteria. The pus formed in boils and abscesses is dead white
corpuscles. Other bacteria act on the body chiefly through the
toxins or exotoxins they produce. These pass into the tissues
surrounding the bacteria, get into the blood, and circulate through

494

HOW BACTERIA ENTER THE BODY 495

the body. For example, diphtheria toxins produce soreness in a
throat on which the diphtheria bacilli are multiplying, and the
blood carries the exotoxins around the body. The heart, kiciney,
or some other remote organ may be affected. The tetanus bacilli
develop their exotoxin at the place where they enter the body.
This toxin then goes to the various tissues, especially the nerves.

Bacterial poisons or endotoxins result from the breaking down
or the disintegrating of certain bacteria. It is thought by some
scientists that these endotoxins are never produced, as are the
exotoxins, by the bacteria themselves, but are only set free during
the breaking down of the bacterial body. The typhoid germs
contain a very powerful endotoxin; tuberculosis, too, has a
strong endotoxin. These are probably due to the breaking down
of the proteins in the bacteria cell and the consequent formation
of substances that are poisonous to the tissues. They are more
correctly called poisonous split-proteins. There is still a fourth way
in which bacteria are related to disease. Protein foods are some-
times attacked by bacteria and are only partly digested or broken
down to a group of products called ptomaines, some of which are
injurious to the body. Ptomaines differ from toxins in that they
are products of food decomposition, while the toxins are products
of bacterial manufacture. The ptomaines are usually formed in
foods under storage conditions in the shop or house, and not in the
body. For example, if protein foods are not properly preserved,
bacteria may attack them, causing disintegration. Partially dis-
integrated fish, crabs, cheese, oysters, or milk often contain
injurious ptomaines and, when eaten, will have a poisonous
effect on the body.

How bacteria enter the body. One of the common avenues of
invasion for bacteria is the alimentary canal. Bacteria of typhoid
fever and tuberculosis are frequently taken in with milk or other
food through the mouth. Pencils, finger nails, and drinking cups
are often responsible for an attack of diphtheria or scarlet fever.

496

DEFENSES AGAINST DISEASE

The respiratory tract furnishes a means for the entrance of germs.
Spray or droplets of sputum sneezed or coughed out may be
breathed in by other people. Germs of pneumonia, diphtheria,
scarlet fever, and colds often enter the body in this way.

Certain other organisms enter the body through wounds or
skin abrasions. These skin openings may be of various kinds.
Cuts, scratches, torn hangnails, and cracked skin are responsible
for the entrance of dirt which may carry not only tetanus germs
but, when present, ringworm (a parasitic mold), hookworms, or
other pathogenic organisms. Insect bites form openings through
which germs may be introduced. The bite of an Aedes mosquito
may transmit yellow fever ; the Anopheles mosquito, malaria ; the
rat flea, bubonic plague ; the body louse, typhus fever ; and the
tsetse fly, African sleeping sickness. The bites of rabid dogs,
cats, wolves, and other animals are responsible for hydrophobia.
Some organisms enter the body through the eyes. If the eyes
are rubbed with an infected hand or dried with an unclean
towel, such diseases as trachoma and pink eye may possibly
result.

Safeguards of the body against disease. The best defense of the
body is the strong natural resistance that accompanies good health.
As long as rules of health are followed, the vitality is likely to be
high. Even though bacteria then invade the body the natural

An unbroken skin is a protection against invading bacteria. If the skin is pricked or other-
wise broken, bacteria may enter and cause an infection.

protective substances and cells tend to control them with success. ,
If resistance is low, due to insufficient air or sunlight, inadequate

SAFEGUARDS OF THE BODY AGAINST DISEASE 497

diet, lack of proper exercise or rest, the body cannot use its natu-
ral protective agencies to the fullest extent, and invading bacteria
gain a foothold in the body, multiply, and bring about a condition
of disorder known as disease.

As long as the skin is unbroken it forms an effective barrier
against the entrance of germs. There is, however, some doubt
whether a bacterium or a Protozoa can gain an entrance only
through unbroken skin. A few parasites such as hookworms are
known to penetrate unbroken skin and may cause a disease which
undermines the vitality, and results in great lethargy and conse-
quent inefficiency. Just as soon as skin is abraded or broken all
kinds of parasites may enter. Broken skin should always be
treated with antiseptics to inhibit the growth of any germs that
attempt to enter. Some antiseptics have an additional value
of promoting healing.

The tears which constantly wash the eye will remove any
bacteria and drain them into the nose, from which they may be
removed. (If bacilli prodigiosus, bacteria that are pigmented red,
be dropped in the eye, they will shortly disappear from the
eye and appear in the nose.) The tears are slightly antiseptic
in action so that they exert a chemical as well as a physical
protection.

The mucous membrane in the nose, mouth, and throat catch
the germs on its sticky surface and prevent them from traveling
further into the body. This mucus is slightly antiseptic in action
and is responsible for the destruction of some germs. When the
membrane has caught germs in its secretion, an irritation is set
up which stimulates sneezing, coughing, or blowing of the nose.
Phagocytes probably destroy some of these bacteria. There are
usually some bacteria found in the nose, throat, and mouth.
As long as the resistance of the body is high and there is no
break in the membrane, these germs do not attack the body.
The body in good condition seems to acquire a certain immunity

498

DEFENSES AGAINST DISEASE

to the germs which it constantly harbors. Saliva as well as mu-
cus is weakly antiseptic. Hairs grow on the lining of the nasal
passages and act as a coarse filter which strains dust particles
from inhaled air. This dust may then be expelled from the nose.
There are specialized epithelial cells in the windpipe and bron-
chial tubes with numerous cilia on their free surfaces, which
wave and fan bacteria or very fine dust particles up and out.
The foreign particles are then coughed out of the throat.

The gastric juice in the stomach probably digests many bac-
teria with the food. The acid of gastric juice sometimes destroys
or inhibits the growth of many germs. Such bacteria then pass
on through the canal with the food. The high acidity in a dog's
stomach will kill bacteria that will cause intestinal infections in
man. Tuberculosis, typhoid fever, and dysentery germs are not
affected by the action of gastric juice and will pass into the small
intestine. Bacteria of putrefaction are always abundant in the
large intestine. If they are too active, intestinal disturbances
result. Most bacteria can work only in an alkaline medium;
therefore to control and inhibit their activity, efforts are made
to introduce acids into the large intestine. The acids in most
foods are absorbed or neutralized before they reach the large in-

Stepping on a tack, rusty nail, or other sharp objects may set up an infection. Tetanus has
been known to get into the body in this way and cause blood poisoning.

testine. A certain bacillus, called the Lactobacillus bulgaricus,
is one of the organisms causing the souring of milk. When this

SAFEGUARDS OF THE BODY AGAINST DISEASE 499

bacillus is taken into the body, it is thought to go into the large
intestine, where it creates an acid medium. Some scientists think
this aids the work of the bacteria of putrefaction and, conse-
quently, clears up auto-intoxication. Recently another strain of
bacteria that sours milk has been found that seems to be more
effective. It is the Lactobacillus acidophilus. These bacteria will
live longer in the intestine than do the Lactobacillus bulgaricus.
There are a number of other conditions that protect the body
against the invasion of germs. Even after germs enter, very
few can cause a disease unless they multiply in great numbers.
The body may be thought of as a great living culture medium.
The inside is dark, moist, warm, and supplies food in the form of
digested foods or tissue cells for invading saprophytes or parasites.
In reality, each specific germ needs a definite combination of con-
ditions. For example, the temperature of the body is not high
enough for the bird type of tuberculosis. Therefore, this type
cannot attack man. The human type grows only between
37° C. and 40° to 41° C. A bird's temperature is much higher
than man's, so that human tuberculosis cannot grow in birds.
Bacteria that ordinarily attack warm-blooded animals are not
likely to affect cold-blooded ones. If, however, the temperature of
the cold-blooded animals is raised, they become susceptible to the
invading germs. Frogs are naturally immune to tetanus, but if
their temperature is raised, they become susceptible to the disease.
Bacteria such as tetanus are anaerobic and grow only in the
absence of air. If tetanus enters a surface wound exposed to
air, it does not multiply. It is only when it enters deep wounds,
where there is no air present, that it sets up an infection. Most
tissue cells offer a high natural resistance to the entrance of germs.
It is only when they are torn or lacerated that conditions are favor-
able for the growth of germs in them. Many bacteria taken in with
food are of the saprophytic type. They make no attempt to at-
tack the tissues but simply feed on food in the alimentary canal.

500 DEFENSES AGAINST DISEASE

When bacteria actually enter the body and get into the blood
or. lymph stream, there are many methods of protection. The

Opsonic* InoleK '[Determination.

Toactericc bacteria,

+, -f

fxxttents serum (control) normal serum.

+ +

"vhite corpuscles -nrhite corpuscles

aq ^- percentage corpuscles <)*
^*C ingesting bacteria — ►• ^^

— =2 patient's opsonic index

Opsonins affect bacteria so that white corpuscles can more easily engulf them. Definite op-
sonic indexes may be calculated from microscopic examinations. A pipette, marked as shown
in the diagram, is used to measure the amounts of bacteria in the patient's serum and white
corpuscles used in the test.

white corpuscles devour bacteria and digest them. Thus, the body
is rid of them. If numbers of bacteria get into the lymph system,
they are frequently carried to a lymph node or gland, where the
bacteria are filtered out. Then a collection of corpuscles attack
the invading germs and destroy them. When a number of
tuberculosis germs are combating white corpuscles in a lymph
gland, the body sometimes deposits a wall of calcium around the
infected center. This removes the whole mass of infected material
from the circulation. Infected lymph glands are sometimes cut
out of the body to prevent a possible reinfection from the tuber-
culosis germs inclosed.

The type of white corpuscle that devours bacteria is the
phagocyte. When germs invade the body, there is an increase
in the number of phagocytes produced in order to check the in-
fection. If blood is examined, and the number of white cor-
puscles is very great, this may indicate an infection in the body.

ANTIBODIES 501

Antibodies. There are many protective substances produced
in the blood in response to the entrance of disease germs or their
poisons. These substances are known as antibodies. Both
toxins and. antibodies are specific for each disease. The toxin
produced by a typhoid bacillus will cause only typhoid and will
never cause diphtheria or any other disease, and the anti-
toxin made by the body to fight diphtheria will have no effect
on any other disease but diphtheria. This is true of all anti-
bodies. Antitoxin is one type of antibody produced in the blood
for the neutralizing of exotoxins. There may be antitoxins in
the blood for diphtheria, others for scarlet fever, and still others
for tetanus. The antitoxins neutralize the toxins produced by
the bacteria and at the same time the phagocytes destroy the
actual bacteria.

Other protective bodies called lysins are present in normal
blood, which actually dissolve the bacteria. The lysins which
dissolve the bacteria are known as bacteriolysins. There are
specific bacteriolysins produced to dissolve diphtheria germs.
Others dissolve typhoid bacilli and still others dissolve meningitis
germs. There are other kinds of lysins besides bacteriolysins.
One kind may dissolve foreign red blood corpuscles and is called
hemolysins. In blood transfusions, if one group of blood is intro-
duced into another group of blood, the hemolysins of the first blood
may dissolve the corpuscles of the second type. Therefore, trans-
fusions are made only among bloods belonging to similar groups.

Certain protective substances are produced in blood to assist
the white corpuscles. For example, agglutinins cause the germs
to stop moving and to gather in clusters or clumps. Then the
phagocytes and lysins can destroy them more quickly. Agglu-
tinins are produced in the body in combating typhoid.

There are also precipitins known to the biologist. Their action
is similar to that of agglutinins. They are specific for different types
of foreign proteins, bacterial and otherwise. Precipitins harden

502 DEFENSES AGAINST DISEASE

or precipitate foreign proteins out of the blood. They are used
as a test for specific bloods, human and other animals.

Opsonins prepare the germs for ingestion by the white corpuscles.
Opsonins seem to combine in some way with the bacteria and so
alter them that the white corpuscles can better engulf them.
There are different opsonins produced by the blood in combating
tuberculosis, boils caused by a staphylococcus, and meningitis.
When opsonins are present, the white corpuscles are better able
to destroy the bacteria. The test for the amount of opsonins
in a patient's blood is a very interesting one. For example, blood
is taken from a patient suffering from tuberculosis, and the serum
is separated from it. The amount of opsonins in this serum is to
be measured. The serum is mixed with white corpuscles from a
healthy animal or person. The white corpuscles are well washed
to make sure that no opsonins are in the mixture before the
serum is added. The serum and white corpuscles are then
added to some tuberculosis bacilli. A little of this mixture is
put on a glass slide, stained, and examined under the microscope.
Then a count is taken, either of the number of bacteria ingested
by the first hundred corpuscles seen, or an estimate of the per
cent of the first hundred white corpuscles seen to have ingested
bacteria. The second estimate is easier than the first because
the white corpuscles devour so many bacteria that in some cases
it is impossible to count them. The estimate is then compared
to normal blood in order to see the increase of opsonins present,
and thus determine the increase in the activity of the white cor-
puscles. Any difference in the white corpuscle activity is attrib-
uted to extra opsonins developed in the patient's blood.

The relation of mental poise to disease. In his farewell address
as the retiring dean of the college of physicians and surgeons of
one of the large universities, a famous doctor stated that the sugar
pill was the outstanding discovery of his generation. He stated
in very decided terms that his long years of experience had con-

QUESTIONS AND SUGGESTIONS 503

vinced him that it was not so much the medicine as the fight
that the patient made, which augmented and strengthened the
defenses of the body. A sense of humor, joy, courage, optimism,
and faith are true defenses against disease. A healthy and con-
tented mind in a properly functioning and intelligently cared for
body is the goal that each reader should strive to achieve.

Questions, and Suggestions

1. Discuss three ways in which bacteria attack the body. Illus-
trate each with a specific disease.

2. Discuss the different ways in which bacteria enter the body.

3. Discuss the natural defenses of the body against the invasion of
bacteria.

4. Discuss the protective substances found in the blood, which pre-
vent the activity of the bacteria in the body.

Supplementary Readings

Broadhurst, J., How We Resist Disease (J. B. Lippincott & Co.).
Greaves, J. E. & E. O., Elementary Bacteriology (W. B. Saunders Co.).
Zinsser, Hans, A Textbook of Bacteriology (D. Appleton & Co.).

CHAPTER XLIX
IMMUNITY

Paul Ehrlich

Eli Metchnikoff

Why can some people resist disease successfully and others haw
very little resistance? What theory of immunity is most generally
accepted? Can all people be made immune to disease?

The ability of the body to resist disease is known as immunity.
To-day, when the emphasis is placed on preventive medicine rather
than curative, immunity is one of the most important phases of
biology. It is a comparatively new science. Two men largely
responsible for founding the science of immunity were Eli Metchni-
koff and Paul Ehrlich.

Eli Metchnikoff. By 1883, Pasteur and Koch had succeeded
in arousing in many scientists an interest in microbes. Metch-
nikoff, a Russian naturalist working in Sicily, studied the way
sponges and starfish digest their food. In investigating these
animals he noticed certain cells moving in their bodies. These
wandering cells acted and looked like amoebas. He fed par-
ticles of powdered carmine to the transparent larvae of starfish
and the wandering cells ingested the particles. Metchnikoff
wondered whether these wandering cells would engulf microbes.
He stuck some thorns from a rose bush into the transparent
starfish. Masses of the wandering cells crowded around the
slivers. He concluded that these cells killed invading germs, and

504

PAUL EHRLICH 505

he gave to them the name phagocytes. He published many
articles and gave lectures concerning his discovery.

Metchnikoff went to Paris to continue his work in Pasteur's
laboratory, Pasteur believed in MetchnikofFs theory of phagocy-
tosis, but Von Behring did not. The latter had already demon-
strated that if tiny quantities of the poisons of tetanus and
diphtheria were injected into rabbits, the rabbits became used to the
toxins and did not become ill. Von Behring thought that chemical
substances in the blood were responsible for this protection. This
experiment was done before the germ of tetanus had actually been
discovered. Von Behring felt certain that the plasma of the blood
and not the phagocytes killed the germs and their poisons.
We now know that both Von Behring and Metchnikoff were
right. Not only do phagocytes devour germs, but blood pro-
duces protective substances, lysins, that dissolve bacteria, and
antitoxins that neutralize bacterial toxins. Metchnikoff formu-
lated the phagocytosis theory of immunity, in which he stated that
phagocytes alone were responsible for immunity. Later he agreed
with Von Behring, that the blood contained other antibodies.

Paul Ehrlich. A German medical student, Paul Ehrlich, was
working on the staining of tissues. He believed that the reaction
of certain bacteria to special drugs or stains might be a method
of killing these bacteria without injuring the organism they were
invading. If he could find stains or dyes with the ability to
attach themselves to certain bacteria, he might introduce a poison
with the dye and thus kill the dyed bacteria. In his staining
experiments he had seen tuberculosis bacilli before Koch had,
but had not recognized them nor described them as such.
When Koch isolated the tuberculosis bacilli, Ehrlich showed
him a simple method of staining them. Ehrlich inoculated
mice with different dyes to see whether he could not make
them immune to a certain disease caused by a spirochaete. In
1893, after over six hundred attempts, he discovered an arsenic

WH. FITZ. AD. BIO. — 33

506

IMMUNITY

compound called 606, which gave immunity to the mice. Ehrlich
tried his 606 on a certain disease in human beings caused by spi-

free.

\%>

A*hocterium

•prodtxxces

r to*cin.

Qribbo&es
ee ii

£& in

•totems on or

Diagrammatic representation of toxins uniting with antitoxins. The toxin has stimulated the
cell to develop an antitoxin which locks or neutralizes the toxin. This is according to the side-
chain theory of Paul Ehrlich.

rochaetes and found that it cured them, also. He called the arsenic
compound salvarsan. He thought the salvarsan united with the
cells of the body and helped to produce an immunity. Instead, it was
later proved that the dye united with the spirochaete and killed it.

Ehrlich was the founder of the humoral or side-chain theory of
immunity, which is still generally accepted by biologists of to-day.
The humoral theory states that protective substances are produced
within the body, usually in the blood, which counteract the effects
of bacteria. Metchnikoff and Ehrlich stimulated research in the
study of immunity. Since then there has been much progress.
To-day, it is one of the big features in preventive treatment.
Many of the cures and discoveries of to-morrow will be built on
the foundations laid by these men.

Types of immunity. Natural immunity is the immunity one has
at birth. It stays with the individual always and, therefore, there

TYPES OF IMMUNITY 507

is no need of an inoculation, nor any danger of an attack of the dis-
ease against which there is the immunity. That there is a natural
immunity of species is shown by the innumerable diseases of animals
to which humans are not susceptible. Similarly, animals con-
tract very few of the human diseases. A natural immunity is,
also, evidenced by various groups of the same species, although
this is somewhat relative. The natives of South America and
Africa are more immune to yellow fever than are the white peo-
ple. Perhaps this is due to a weeding-out process during which
the fittest has acquired an immunity while the unfit died. This
does not always explain natural immunity, however. Measles is
a mild disease with white people, but fatal to natives of certain
South Sea islands. Jews are more immune to tuberculosis than
Irish and English people. Eskimos, Indians, and Negroes are
highly susceptible to tuberculosis. The North American Indian
seems to be immune to scarlet fever. The colored people in the
southern part of the United States seem to have a natural resist-
ance to diphtheria. This type of natural immunity is often
called racial immunity. Certain members of the same race show
a natural immunity to disease while others do not. For example,
some children seem naturally immune to diphtheria as seen in
their reactions to the Schick test. Whether natural immunity
is the result of natural selection, or whether it can be explained
by environmental conditions, is still not decided.

Acquired immunity differs from natural immunity in that it is
developed during the lifetime of the individual. There are two
types of acquired immunity, active and passive. Active acquired
immunity is produced by the body itself as a result of having the
germs or the toxins of a disease enter the body. There are three
ways in which this may be accomplished. (1) By an actual attack
of the disease. If this method produces immunity for any appre-.
ciable length of time, it is likely to last for life. For example, once
a person has had typhoid, smallpox, or diphtheria he is likely to

508 IMMUNITY

develop an active immunity which lasts for life. (2) By 'vaccina-
tion. The introduction of dead or attenuated (weakened) germs
of the disease, in small doses, stimulates the body to produce its
own antibodies. In vaccinating against typhoid and yellow fever,
the dead organisms are used. In smallpox, germs weakened by
passing them through a cow are used to make up the vaccine.
This is known as animal passage. In rabies, the germs are
attenuated by drying them. Germs may also be weakened by the
application of slow heat or by growing them on media that are
not quite favorable. In each of these cases the body cells respond
to the inoculation by producing antibodies. (3) By the injection
of toxin from which the bacteria have been filtered. Sometimes the
toxin has some antitoxin mixed with it to dilute and make it
safer, as in diphtheria toxin-antitoxin. Sometimes small quan-
tities of the toxin itself are used, as in scarlet fever immunization.
Here, again, the body produces antibodies. All actively acquired
immunity is usually lasting in its effects. Active immunity takes
some time to produce because the cells require time to make
their reactions.

Passive acquired immunity is obtained by the injection of anti-
toxins or immune serums from the body of another person or an
animal. Such immunity is immediate in its effects, but it does not
last for very long. The antitoxin is already prepared. It sets to
work promptly neutralizing the toxin present. The injection of
such material does not stimulate the body to produce its own
antibodies and hence this immunity lasts for only a short time.
It is used in the actual treatment of the disease or to protect some
one who has been exposed. For example, diphtheria patients and
their families are given antitoxin. An immune serum is frequently
given for pneumonia and infantile paralysis.

The immunity of to-morrow. A very recent investigator, d'He-
relle, has demonstrated the presence of what he has called a bac-
teriophage, a kind of super bacteria that destroy other bacteria

QUESTIONS AND SUGGESTIONS 509

and produce an immunity. Experiments have been made in
France and are now being conducted at Harvard and Yale uni-
versities with this material. Watch for results of the work. The
problem of immunity is still far from its solution. Scientists are
just beginning to solve many of the questions. You who are to
be scientists of to-morrow will have opportunity for research in
this and many other fields of biology.

Questions and Suggestions

• 1. Discuss Metchnikoff's experiments with phagocytes.

2. Give a report on the life and work of Metchnikoff.

3. Discuss Ehrlich's experiments with dyes and chemicals on
bacteria.

4. What theory of immunity was founded by Ehrlich ?

5. Give some interesting facts about the life and work of Ehrlich.

6. Discuss natural immunity ; acquired immunity.

7. What test may be used to see whether a child is or is not
naturally immune to a certain disease ?

8. What specific inoculations should be given all children to make
them actively immune to diseases with which they come in contact?

9. What specific inoculations should be given a person who is
traveling to make him actively immune to diseases with which he
might come in contact?

10. State two differences between active and passive immunity.

11. Under what conditions will a person be actively and passively
immunized against diphtheria ?

12. Answer some objections that may be currently raised against
immunization.

CHAPTER L
TAXONOMY

"Kingdom

Animal

^Ph^lum

Chor&ata

Class

"Mammalia ■

OrdL&r-

Carnivora

T$zm'\W_

"Feliaaex

Genics

Felis

[ Species Somestica

' iTj&ivi&ual "from.

Linnaeus

A cat named Tom

How can the many plants and animals of the world be identified f
What is the purpose of identification? What is taxonomy? What
contributions made by scientists have helped to systematize the classi-
fications of plants and animals ?

It is said that Alexander the Great was a pupil of Aristotle, the
Father of Biology. Alexander held his teacher in the highest
esteem, and, during his campaign and conquests, kept a group of
couriers to carry unusual plant and animal forms back to his friend
and teacher. These specimens came in such large numbers that
Aristotle had to devise a means of caring for them in an orderly
manner. He used a system of classification that was largely based
on the habitat of the organisms. For his animals he had eight
groups, four of which were blood-containing, and known as mam-
mals, birds, egg-laying quadrupeds, and fishes; while four were
bloodless, namely, squid-like animals, Crustacea, insects, and
animals with shells.

The binomial system of Linnaeus. Various other scientists
changed this system, but Carolus Linnaeus, a Swedish natu-
ralist, devised the system upon which the modern method of
classification is based. Before his time, in order to describe a
kind of grass and not confuse it with other forms more or less

510

THE BINOMIAL SYSTEM OF LINNAEUS 511

like it, a descriptive name similar to the following was used : Gramen
Xerampelino, Miliacea, praetenius ramosaque sparsa panicula, siya
Xerampelino cogener, arvense, aestivum. Carolus Linnaeus^ was
an assistant to the Professor of Botany in the University of
Upsala, Sweden. While cataloguing plants, he had come across
many descriptions such as the one just given. He realized that
such a name was too long and inconvenient and he initiated a num-
ber of reforms in the existing scheme of classification. He gave
the name " Pea bulbosa " to this plant. In his system which he
called the binomial nomenclature, two names sufficed to dis-
tinguish this organism from all others. One .name designates
the genus of the plant or animal, the other the species. All
organisms that have similar characters are grouped together and
this group is called a genus. The' name given them is the generic
name. The genus is subdivided into groups with varying char-
acters called a species and the name given is the specific name.
The generic name for all the members of the cat tribe is Felis. The
genus Felis is subdivided into the species such as leo (lion), par-
dus (leopard), domestica (house cat). Therefore, the lion is
known as Felis leo, the leopard as Felis pardus, and the house
cat as Felis domestica. The initial letters of the name of the
genus is always capitalized and that of the specific name is written
with a small letter.

What a task Linnaeus undertook ! He published his most impor-
tant work, Systema Naturae, in twelve editions and like all scien-
tists of his time, wrote the descriptions in Latin. This practice
continued until very recently. Exchanges of scientific papers on
classifications could be made throughout the world in a common
language. Recently, scientists have employed their mother tongue
for the description of any new creature. When the discovery is an
important one, the paper is translated by those who need the data.
Linnaeus died in 1778, but his work lives on and, with a few modi-
fications, is still used to-day.

TAXONOMY

N. Y. ZoSlogical Society
There are marked differences in size, shape, and habits of present day mammals. The
giant anteater, Myrmecophaga jubata, is a native of tropical America. Its coarse hair is almost
bristle-like in structure. The long narrow snout and a long tongue enable it to lick up in-
sects.

The basis of the classification of to-day. The scientist of to-day
knows many more animals than Aristotle or Linnaeus knew.
There are probably more than a million different kinds of ani-
mals now known, and nearly as many plants. With the method of
identifying and classifying animals and plants in an orderly and
scientific manner there has grown a division of biology, taxonomy,
that is concerned with this classification. Taxonomy (from taxis
— arrangement; nomos — law) is the division of biology that
has to do with the classification of animals and plants on the basis
of fundamental similarities. The modern method of classifica-
tion of plants and animals does more than catalog animals for
the convenience of the scientists. It expresses a kinship and rela-
tionship. The relationship of plants and animals has been de-

'the basis of the classification of to-day 513

termined from their structure, embryology, habits', habitat, ability to
crossbreed with related forms, and from certain other facts.

By structure is meant the shape and arrangement of the parts of a
plant or animal. Certain plants are grouped together because they
have chlorophyll ; certain animals are classified together because
they have six legs. The embryology of a plant or animal refers to
its development from the time it is first formed until it is a full-
grown adult. A caterpillar looks somewhat like a worm which is
really one of the stages in the life history of an insect. Plants and
animals that have similar embryological developments are closely
related; those with dissimilar embryological developments are
not closely related. Animals and plants which are closely related
usually have some similar habits. In general, most water plants

N. Y. Zoological Society
The duckbill (Ornithorhynchus anatinus) is an egg-laying mammal, native of Australia. It is
covered with dark fur, and has a bill and five-toed webbed feet.

514

TAXONOMY

are closely related. Animals that carry their young in pouches are
classified together. Birds that have wading habits belong to the

N. Y. Zoological Society
The Armadillo (Tatu novencinctum) is covered with a bony shell. Some species can curl up
into a ball, presenting the armor on all sides.

same group. Habits alone do not determine classification ; other
facts must be considered. The whale is frequently thought of as
a fish because it swims and lives in the water. Actually it is a
mammal because it suckles its young. When animals or plants
crossbreed with each other, they are usually found to be closely
related. For this reason successful crossbreeding is only possible
with those forms that are closely related. For example, the
horse and donkey will crossbreed and produce a mule. The mule
is probably always sterile, and will not produce offspring. Dogs
and wolves will crossbreed and the hybrid offspring will repro-
duce. Consequently, dogs and wolves are thought to be more
closely related than are horses and donkeys.

The Law of Priority. So many modifications of Linnaeus' sys-
tem of classification arose that confusion resulted. An Interna-
tional Commission on Classification was founded in 1895. Its pur-
pose was to draw up a set of rules which would be accepted and

THE LAW OP PRIORITY

515

adopted by the scientists of the entire world. One of the basic
rules formulated by this commission is the Law of Priority. This
has to do with the scientific name each animal and plant^is to
bear. Suppose an unfamiliar microscopic animal is observed. The
scientist draws it, photographs it, perhaps he kills it, and studies
it as stained and sectioned material. He then consults the de-
scriptive classification organized since 1895 and seeks the proper
place to catalog his specimen. If the specimen is not similar to
any known organism, the scientist gives it a generic and specific
name, writes a description, and publishes his findings. If no
other scientist reading his paper has ever come across it or seen
a description of it elsewhere, this scientist is thereafter credited
with the discovery. He has added a new creature to the list of
known organisms.

Insectcc

*Kyriccpoola Onychoptaonec

rjtxcny-va^i*^ Ws -me surviving

brings present

ensfflang legk aquatic, artTit-oTDOct^

G.rachni&cc

Crustacea

The phylum Arthropoda is subdivided into five present-day classes. There are many fossil
arthropods, some of which are quite unlike present-day forms.

The method of the classification of to-day. All living things are
placed into one of two kingdoms, the plant kingdom or the ani-

516

TAXONOMY

mal kingdom. These two kingdoms are further divided. Cer-
tain outstanding likenesses enable a scientist to divide the plant

Museum of Natural History
The Crustacea vary in size and shape from microscopic representatives to lobsters weighing

nearly fifty pounds.

kingdom into four divisions called phyla (singular, phylum). In
this book the animal kingdom will be divided into ten phyla.
The various phyla have been carefully analyzed and compared,
and finer groupings, called classes, made. Again a finer sorting
is made and the classes are split into orders. Certain char-
acters again permit a subdivision of the orders into genera. The
genera are separated into groups showing very close relationship.
These are the species. They are very much alike, but may still
differ slightly in form, habitat, or distribution.

One phylum of animals, the arthropoda, is distinguished from
the other ten phyla in that all of its members are segmented,
have an exoskeleton and jointed legs. One of the classes of the
phylum arthropoda has a characteristic exoskeleton impregnated

CLASSIFICATION OF TO-DAY 517 ♦

with lime. The organisms with a lime skeleton are put in the class
called the Crustacea. All the arthropods with' lime skeletons and
ten legs are then grouped into an order, the Decapoda. In this
order are found the crabs, lobsters, crayfishes, and the like. The
different members of the order Decapoda are then separated into
various genera and species. The sea-living lobster belongs to the
genus Homarus, while the land-living and fresh-water crayfish
belongs to another genus, Cambarus. There are different species
of lobsters in the genus Homarus. The North American lobster
belongs to the species americanus which is slightly different from
the European lobster, vulgaris. The farther down the scale of
classification the closer is the relationship. Species are more
closely related than genera and, in turn, genera are more closely
related than orders, etc.
Phylum Arthropoda.
Class Crustacea.
Order Decapoda.
Genus Homarus.
Species americanus (American Lobster).
The Paramecium may be similarly classified.
Phylum Protozoa (one-celled animal).

Class Infusoria (numerous hairlike processes used for loco-
motion and feeding, presence of fixed openings for
food ingestion and the extrusion of solid wastes).
Order Holotrichia — animals with cilia of equal length dis^
tributed over the entire body.
Genus Paramecium.
Species caudautum.
Using this modified Linnaeus method, let us consider a butter-
cup. It belongs to the great branch of phylum of the plant king-
dom known as the Spermatophyta. It is placed in the class Angio-
spermae. It is of the genus Ranunculus, and there are many
species,

518 TAXONOMY

The classification of man is another example.

Phylum Chordata (most members have backbones and have
central nerve cords).
Class Mammalia (presence of hair ; the young are fed on
milk ; a muscular diaphragm separates the thorax from
the abdomen).
Order Primates (erect or nearly so).
Genus Homo.
Species sapiens.

Classification of plants.

few

icloply

The plant kingdom is divided
into four large groups called
phyla. The flowering group
of spermatophytes are the most
recent plants.

I. Phylum THALLOPHYTA (thallus — young branch ; phyton
— plants). Includes very simple plants, sometimes single-celled,
but more often many-celled; some have chlorophyll, others are
without this green material ; none have roots, stems, or leaves.

There are two subphyla, Fungi and Algae. The Fungi are
non-green plants of very great economical importance. There
are four classes found in the subphylum fungi.
Class I — Fission fungi. Bacteria.
Class II — Tube fungi. Have tubular bodies. Example is

bread mold.

CLASSIFICATION OF PLANTS 519

Class III — Sac fungi. Produce spores in a sac. Examples
are the yeasts, powdery mildews, and many others.

Class IV — Club fungi are so-called because their spores are
produced upon a club-shaped structure. Mushrooms, puffballs,
smuts, and rusts belong to this group.

The subphylum Algae includes the chlorophyll-bearing thallo-
phytes. In some forms the chlorophyll is masked by some other
coloring matter. They range from single-celled forms to filamen-
tous colonies or even long ribbon or rope-like masses many feet in
length. They are nearly all aquatic. The subphylum Algae is
subdivided as follows :

Class I — Blue-green algae contain a blue pigment in the
cells in addition to the green color. Examples are Nostoc pru-
niforme and Oscillatori violacea.

Class II — Green algae are of countless forms, unicellular,
filamentous, platelike, and in irregular masses of cells. There
are both fresh-water and salt-water forms, and others live on
land. One form will grow on snow patches. Pleurococcus vul-
garis and Vaucheria terrestris are examples.

Class III — Brown algae are nearly all marine plants.
They are the commonly known seaweeds.

Class. IV — Red algae are mostly marine. Our most deli-
cate and beautiful seaweeds belong to this main class.

II. Phylum — BRYOPHYTA (Gr., bryon — moss; phyton —
plant) . Contains only two classes, the liverworts and the mosses.
These plants are small and live mostly on land. They show a
greater development of tissues than the algae and may be
either thallus-like (liverworts) or have stems with rootlike pro-
jections and very simple leaves. They reproduce by forming
spores.

III. Phylum — PTERIDOPHYTA (Gr., pteris — fern). This
includes a group which, when the world was younger, played a
very important part in the vegetation on the earth. Most coal is

520 TAXONOMY

made from ferns of the past. They have true roots, stems, and
leaves, but reproduce like the mosses, by forming spores. The
Pteridophyta include three classes : the true ferns, the horsetails
(Equisetum), and the lycopods or club mosses.

IV. Phylum— SPERMATOPHYTA (Gr., sperma— seed). The
seed-bearing plants are grouped into two subphyla. The Gym-
nospermae (Gr., gymnos — naked), or naked-seeded plants,
include a small group related to the ferns on one side and the
flowering plants on the other. Two classes are found in this sub-
phylum: the Cycads, of which the so-called sago palm is an
example, and the Conifers or evergreens, as pines, spruces, firs,
hemlocks, cypress, and others. The evergreens include the
sequoias, the largest and oldest trees. The subphylum Angio-
spermae (Gr., angeion — case or vessel), or true flowering plants,
include the common grasses and grains, flowering trees and shrubs,
and flowering plants. It is divided into two sub-classes, Mono-
cotyledones and Dicotyledones.

The classification of animals.

60.0 00 070rddCtc£Vp or .i A,r-cc

v species / A? JsFTjZw

-isooo^^l AnneliSLoc

The number of species given
in the diagram is approximate
and not exact.

Phylum I —r PROTOZOA (Gr., protos — first ; zoon — animal) .
Single-celled animals without true organs, or tissues. Occasionally

THE CLASSIFICATION OF ANIMALS 521

protozoa are colonial, in which case the unit cells of the colony
are all potentially alike. There are four classes of protozoa.

Class I — Rhizopoda (root-footed) . These cells have no fixed
form. The Amoeba proteus is one of the best known animals in
this class. The Amoeba histolitica causes a disease of the mouth.
Amoeba dysentericus causes summer complaint in children.

Class II — Mastigophora. Move by one or more long, whip-
like threads of cytoplasm called flagella. Euglena viridis is an
example.

Class III — Sporozoa. Parasitic Protozoa, usually lacking
motile organs or mouth. They reproduce by spores. Example :
Plasmodium malariae.

Class IV — Infusoria. Animals which have many vibratile
processes (cilia), a cuticle, and fixed mouths and anal spots.
Paramecium caudatum, Vorticella.

Phylum II — PORIFERA (Lat., porus — pore; ferre — bear).
Many-celled animals, so arranged as to form two layers of cells.
Their bodies are usually penetrated by numerous pores. The
cells of the body are supported by a skeleton of " spicules " or
material called spongii." There are three classes.

Class I — Calcarea. Sponges with spicules composed of cal-
cium carbonate. Example : Grantia.

Class II — Hexactinellida. Sponges with spicules of silica
triaxon in form. Glass sponges. Venus flower basket.

Class III — Demospongia. Sponges with skeletons of spicules
of spongin or a combination of spongin and silicon. The bath
sponge is an example.

Phylum III — COELENTERATA (Gr . koilus — hollow ; enteron
— intestine) . Composed of animals made of two layers of cells
invaginated to form a gastrula or internal cavity; they have a
mouth surrounded by tentacles and no anus. They are pro-
tected by stinging cells which also aid in killing prey.

Class I — Hydrozoa. Single animals like Hydra fusca or colo-

WH. FITZ. AD. BIO. — 34

522 TAXONOMY

nial animals, as Obelia weismania. These animals reproduce by
buds, and by eggs and sperms. In the colonial types, certain
buds of the original colony are free-swimming jellyfish. These
produce the eggs and sperms.

Class II — Scyphozoa. Marine jellyfish, large in size. Ex-
amples are Aurelia flavidula and Portuguese man-of-war.

Class III — Anthozoa. Large hydra-like animals, single or
colonial, usually attached, with many tentacles arranged in
circles of multiples of five. The sea anemones and corals are
the best known examples.

Phylum IV — PLATYHELMINTHES (Gr., platys — flat ; hel-
minthos — worm), or flatworms. Three-layered animals, bilat-
erally symmetrical, usually small, ribbon- or leaf-like, flat, and
live in water. Most flatworms are parasitic. Examples are
tapeworm and liver fluke.

Phylum V — NEMATHELMINTHES (Gr., nematos — a
thread), or round worms. Three-layered, elongated, thread-like
animals, often parasitic. Vinegar eels, the horsehair worm, the pork
worm or trichina, the threadworm, and the hookworm are examples.
Phylum VI— ECHINODERMATA (Gr., echinos — hedge hog;
derma — skin). Radially symmetrical, spiny-skinned animals
which live in salt water, more complicated in structure than the
worms. Five classes :

Class I — Asteroidea. Starfishes.

Class II — Ophiuroidea. The brittle stars or snake stars.
Class III — Echinoidea. Sea urchins.
Class IV — Holothuroidea. Includes the sea cucumbers.
Class V — Crinoidea. Stone-like, deep-sea forms, now almost
extinct. Sea lilies and sea feathers are examples.
Phylum VII — ANNELIDA (Lat., anellus — a ring) . Bilateral,
segmented worms; composed of body rings or segments. The
digestive tract is a tube within a tubelike body. No jointed
appendages. There are two classes :

THE CLASSIFICATION OF ANIMALS

523

Class I — Archiannelida. Primitive marine worms without
parapodia or setae. Example: Polygordiusr

Class II — Chaetopoda. Bristles along the body. Examples
are the earthworm or sandworm.

Class III — Hirudinea. Without bristles and having suckers
at both ends of the body. Examples are the leeches.
Phylum VIII. MOLLUSCA (Lat., mollis — soft). Soft-bodied
unsegmented animals, often provided with a shell which is secreted
by a part of the body.

Class I — Gastropoda (bellvrfooted). With or without shells,
which, when present, are of one piece and coiled. Snails, whelks,
and slugs.

Class II — Pelecypoda (hatchet-footed). Shells in two
valves or parts. Clams, oysters, scallops, and mussels.

Class III — Cephalopoda (head-footed). Foot partly sur-
rounds head and bears tentacles or grasping organs. Squids,
octopuses, and cuttlefishes.

Phylum IX — ARTHROPOD A (Gr., arthros — joint; pous —
foot). Animals are segmented, and have chitinous exoskeletons
and jointed appendages. They live in water, on land, in the air,

The reptiles are legless vertebrates with a skin covering made of scale-like plates.

524 TAXONOMY

or in all three places. Most of them undergo a metamorphosis.
There are five classes :

Class I — Onychophora. Primitive air-breathing arthropods
with tracheae and nephridia. Peripatus capensia.

Class II — Crustacea. Breathe by means of gills. The head
and thorax are fused ; two pairs of antennae. They have a
" crusty " exoskeleton, strengthened with lime. Examples,
crabs and lobsters.

Class III — Myriapoda (numberless legs). Have long bodies
with many segments and many paired jointed appendages ;
breathe by tracheae., Centipedes and millipeds are examples.

Class IV — Arachnida (Gr., arachne — spider). This group
has no antennae, four pairs of legs, and a pair of clawlike
appendages on each side of the mouth. Head and thorax com-
bined as in Crustacea. - Breathe by book-gills, book-lungs, or
tracheae. The spiders, daddy-long-legs, scorpions, mites, and
ticks are in this class.

Class V — Insecta. The largest class of animals. Body seg-
mented ; three body regions, head, thorax, and abdomen ;
three pairs of jointed legs; usually compound eyes; breathe
through tracheae or air tubes. Insects.

Phylum X. — CHORDATA (Lat., chorda — cord). Animals
having a skeletal axis, gill slits in embryo or adult, and a nerve
cord dorsal to the alimentary canal. This phylum is divided into
four subphyla, one of which is the Vertebrata in which a nerve
cord is protected by a segmented, bony spinal column. These
vertebrates are divided into seven classes.

Class I — Cyclostomata. Eel-like vertebrates with round
mouths and without functional jaws, without scales and fins.
Lampreys and hagfishes.

Class II — Elasmobranchii. Fishlike vertebrates without a
bladder, with jaws, and with a cartilaginous skeleton. Sharks,
rays, and skates.

THE CLASSIFICATION OF ANIMALS,

525

The relationships of the backboned animals is often shown by a tree. Animals supposed to
have appeared early are on lower branches. The very recent animals and man are on the tips
of the higher branches. Related animals are found on the same or nearby branches. ^

Class III — Pisces. The fishes. Aquatic, cold-blooded verte-
brates breathing by means of gills, having an air bladder, a
two-chambered heart, and a skinlike exoskeleton of scales.

Class IV — Amphibia. Cold-blooded vertebrates breathing
by means of gills in some stage of their life history. Skin is
not covered with scales, the heart is three-chambered. Most

526

TAXONOMY

amphibians undergo a complete metamorphosis. The larvae form
comes from the egg and live in the water and possess gills. Frogs.
Class V — Reptilia. Cold-blooded vertebrates usually cov-
ered with scales, breathing throughout life by means of lungs.
The heart is three-chambered. Lizards, snakes, and turtles.

Class VI — Aves. The birds. Warm-blooded vertebrates cov-
ered with feathers. Front limbs are wings ; they have air spaces
in the bones, no diaphragm, and a four-chambered heart. Birds
lay eggs with a shell of lime, and usually care for their young.
Class VII — Mammalia. Warm-blooded animals covered
with hair, at some stage. Usually have mammary glands and
suckle the young. They have a diaphragm between the thorax
and abdomen. This class may be divided into eleven orders :
Order 1 — monotremata. Egg-laying mammals. Duck-
bill, spiny anteater.

Order 2 — marsupialia. Carry immature young in a
special abdominal pouch. Kangaroo, wombat, opossum.

N. Y. Zodlogical Society
Darwin did not say that man came from monkeys. He and other evolutionists believe that
there is a common ancestor 'of man and certain of the apes.

Order 3 — Edentata. Toothless or with very simple teeth.
Hairy anteater, sloth, armadillo.

THE CLASSIFICATION OF ANIMALS 527

Order 4 — cetacea. Adapted to marine life. Whale, por-
poise, dolphins.

Order 5 — sirenia. Fishlike in form ; pectoral "limbs
paddle-like. Examples : manatee, dugong, sea cow.

Order 6 — rodentia. Incisor teeth chisel-shaped, usually
two above and two below. Examples: beaver, rat, porcu-
pine, rabbit, squirrel.

Order 7 — ungulata. Hopfs ; teeth adapted for grinding.

a. Odd-toe. Horses, zebras, rhinoceros.

b. Even-toe. Ox, sheep, antelope, camel, giraffe, deer,

pig, hippopotamus.

c. Proboscidea. Elephants.

Order 8 — insectivora. Small, insect-eating, furry or
spiny covered ; long snout. Moles, shrews, hedgehog.

Order 9 — chiroptera. Fore limbs adapted to flight,
teeth pointed. Example : bat.

Order 10 — carnivora. Long canine teeth, sharp and
long claws. Examples : dog, cat, lion, bear, seal, and sea lion.

Order 11 — primates. This order of animals includes man.
Erect or nearly so, fore appendages provided with a hand.
Lemurs, monkeys, baboons, mandrills, apes, gibbons, orang-
utans, chimpanzees, gorillas are in this group.

a. Lemuroidea. Small squirrel-like animals living in trees

and bushes. The lemurs and marmosets.

b. Cebidae. The New World monkeys. Grasping tails and

flat noses. Howling monkey, spider monkey, capuchin.

c. Cercopithecidae. The Old World monkey. Tail not

grasping, or short ; nostrils pointing downward. Dis-
tinct, opposable thumb. Baboon, mandrill.

d. Simiidae. The anthropoid (man-like) apes. No dis-

tinct tail; arms longer than legs. Gibbon, orang-
utan, chimpanzee, and gorilla.

e. Hominidae. The human race.

APPENDIX

HOW TO PREPARE CULTURES OF PROTOZOA

Mixed cultures. Ordinary clear pond water may be used. Water
take^n from an aquarium, in which plants have been growing, fre-
quently contain Protozoa. If tap water is to be used, let it stand in
open vessels for at least a week in order to let the chlorine or other
antiseptic gases escape.

Cultivation of Paramecia. Prepare a hay infusion by cutting
timothy hay stems into short lengths. Fill a six-inch by eight-inch
sterilized battery jar one half to two thirds full of water and add a
small handful of the cut hay stems. Set the jar on a table in medium
light and do not cover. After a few days a scum will form on the
surface of the water. First bacteria and then Protozoa including
Paramecia, will appear. The Protozoa will feed on the bacteria. A
succession of forms will appear within a space of three to four weeks.

Pure culture of Paramecia., Cut timothy hay stems into short
lengths. Boil these with plenty of distilled water until the water turns
brown. Three different concentrations of culture media should be
prepared. Sterilize all glassware by boiling.

Solution 1 — Put two heaping tablespoonfuls of boiled hay in a
large beaker containing two thirds of the undiluted hay water.

Solution 2 — Put one tablespoonful of boiled hay in a large beaker
containing diluted hay water (half hay water, half boiled water,
plain).

Solution 3 — Put a heaping teaspoonful of boiled hay in a large
beaker containing two thirds of diluted hay water.

Let the solutions ripen, exposed to the air for about a week. Then
inoculate with a pure culture of Paramecia. 1 Check your solutions
carefully so that you will know which one gives the best results.

Cultivation of amoeba. Water weed method. — Boil some fresh
water plants, Elodea or Ceratophyllum. Place a very few of these

529

530 APPENDIX

dead, though still green, water plants in the bottom of a 4 by 6-inch
battery jar which has been carefully sterilized, and pour on aerated
distilled water to a depth of 2\ to 3 inches. It is very important not
to use too much plant material. In general, sufficient weed material
should be added to cover the bottom with a greenish layer. In addi-
tion, place in each culture 8 or 10 wheat grains which have been thor-
oughly boiled. After the culture has stood for one week, add a pure
culture of amoebas. If you have no amoebas, look for them in their
natural habitat, e.g., pond or aquarium. Only a very small variety
of amoebas are usually found in such places. If a greater variety is
preferred, they may be purchased from a biological supply house. 1
By re-culturing from time to time amoebas can be kept for the entire
school year.

The amoeba culture should be kept in medium light and in a cool
room where the temperature does not vary greatly. An optimum
of 20° C. (68° F.) is satisfactory. It is difficult to keep amoeba cultures
during the summer because of the high temperature. However, if
the cultures are stored in a cool, fairly well-lighted basement, the
animals will usually survive.

Upon the bottom of the properly prepared amoeba culture, there
forms a greenish layer of loose material. Microscopic examination
will show that this layer is rich in diatoms, desmids, and other plant
cells and it is on and in this bottom layer of greenish material that the
amoebas feed and multiply. Within a week or, at most, two weeks
after inoculation the culture should be rich in amoebas which will
generally live and reproduce for some time.

The main point to be emphasized in connection with this type of
culture is that the water must remain clear. That is, it should not
become cloudy or show evidence of fermentation in the formation of a
surface film or scum. If the culture develops either of these charac-
teristics, too much plant material is present and such a culture should
be thrown out and a new one started.

1 Satisfactory cultures of Paramecia and amoebas may be obtained either
from the New York Biological Supply House or J. D. Dawson, College of
the City of New York, New York.

APPENDIX

531

Fuel Value of Certain Foods 1

Name of Food

Milk and Milk Products:
Milk, whole ....
Butter milk ....
Cheese, American . .
Cheese, cottage . .
Cream, thin ....

Butter

Ice cream ....

Oils:

Olive oil

Cottonseed oil . .

Bread and Cereals:
Bread, white . . .

Graham Bread . . .

Boston brown bread

Bran, wheat . . .
Corn meal, cooked
Hominy grits, cooked
Macaroni, cooked .
Oatmeal, cooked .
Rice, brown, steamed
Rice, white, steamed

Eggs:

Egg, whole . .

Egg, white . . .

Egg, yolk . . .

Meat, Fish and Poultry:
Bacon, cooked . .

Mrasure

ipt.
ipt.

1 in. cube
3* T.
2T.

pat, 1 T.
I cup

IT.
IT.

1 slice
3 X3i
X 1 in.
1 slice
3i X2
Xf in.
\ in. slice
3 in. diam.
J cup
f cup
i cup
h cup
f cup
I cup
f cup

1 egg
1 egg
1 egg

4-5 small
slices

Total

Protein

Fat

Calories

170

. 88

100

, 1

320

202

100

—

100

Carbo-
hydrate
Calories

48
48

3
11

105

43
85
63
42
45
83
90

1 Adapted from Charts in Amer. Red Cross pamphlet, "Food. Why?
What? How?"

532

APPENDIX

Fuel Value of Foods (Continued)

Name of Food

Measure

Total
Calories

Protein
Calories

Fat
Calories

Carbo-
hydrate
Calories

Meat, Fish, and Poultry —

Continued

Beef, lean, broiled

2 slices,

200

104

—

4X3
X H in.

Chicken, roast ....

1 slice,
4X2i
X i in.

100

Fish, lean, broiled . . .

1 slice,
4X2}
X 1 in.

133

Ham, boiled

1 slice,
4f X6
X£in.

150

106-

~~-

Lamb, chop, broiled . .

1 chop

100

—

Lamb, roast

1 slice,

100

" —

3iX4i
X£in.

Liver, calf, broiled . .

medium
size

serving

100

—

Mutton, roast ....

1 slice,
3X3f
Xi in.

100

Oysters, raw ....

Pork chop, lean, broiled

1 chop

200

136

—

Veal leg, lean, broiled

1 serving

150

105

—

Vegetables:

Asparagus

4 stalks
4 in. long

» 1

Beans, lima, dried . .

i cup

200 '

v 8

150

Beans, lima, fresh . . .

h cup

100

Beans, dried

i cup

171

118

Beans, string, fresh . .

| cup

Beets

i cup
in cubes

Cabbage, chopped . . .

i cup

ID"

APPENDIX

533

Name of Food

Measure

Total
Calories

Protein
Calories

Fat
Calories

Carbo-
hydrate
Calories

Vegetables — Continued

Carrots, cooked . . .

2 medium

Cauliflower

l\ small

head

Celery

i-cup

— .

Corn, fresh

1 ear, 6 in.

Corn, canned ....

1 cup

100

Cucumber

f cucum-
ber

Dandelion greens . . .

§ cup

Lentils, dried ....

3f T.

150

102

Lettuce

J head

Okra

5 to 6 pods

Onions

3 to 4
medium

100

Parsnips

i cup
in slices

1 cup

253

177

Peas, fresh

I cup

Potatoes, white, boiled

1 medium

100

15 min.

Potatoes, sweet, baked .

1 medium

200

178

Rutabaga, raw ....

f cup

Spinach, cooked . . .

f cup

Squash, cooked, summer

i cup

Tomatoes, fresh . . .

1 small

Turnips, cubes, raw . .

i cup

Fruits, Fresh:

Blackberries ....

i cup

100

Cantaloupe . .

| melon

—

• Cherries, stoned

icup

Cranberries . .

i cup

Grape fruit . .

h large

100

Grapes, white .

100

Huckleberries .

i cup

Lemon juice . .

IT.

—

Olives, green

4 medium

. . 41

Oranges . . .

1 medium

534

APPENDIX

Fuel Value of Foods (Continued)

Name of Food

Fruits, Fresh — Continued
Orange juice . . .

Peaches ,

Pears

Pineapple ....

Plums ....
Raspberries . .
Rhubarb . . .
Strawberries

Fruits, Dried:
Apricots . . .
Dates, unstoned
Figs . . . .
Prunes . . .
Raisins . . .

Nuts:
Almonds

Peanuts

Pecans . . .
English walnuts

Sugar and Sweets
Sugar . . .
Honey . .
Maple syrup
Molasses . .
Corn syrup .
Gingerbread, plain

Sponge cake (2 eggs, hot
water)

Measure

i cup
3 medium

2 medium
2 slices

1 in. thick

3 to 4 large

f cup
1 cup
f cup

9 halves
3 to 4
3 large

4 medium
i cup

12 to 15

nuts
20 to 24

nuts

12 meats

8 to 16

meats

IT.

2T.

2T.
lfT.
piece,
1 Xlf
X2in.
piece,
3 X2f
X I'm.

Total
Calories

50
100
100
100

100
33
25
50

100
100
200
100
100

100

100
100

50
100
133
133
100
200

150

Protein
Calories

4
4

5
3
2
5

7
2

10
3
3

5
11

Fat
Calories

87
82

42
10

Carbo-
hydrate
Calories

APPENDIX 535

HEALTH HABIT SCORE SHEET

Adapted, by permission, from An Analysis of Instruction for Habits
and Practices in Health and Accident Prevention prepared by E.
George Payne (Lyons & Carnahan, publishers).

Directions. The teacher should go over the outline point by point
and explain any items upon which the students wish help. The habits
and practices may be checked at any time, near the beginning and
the end of each semester. The scoring should be recorded in the
biology note book. Each student should aim to make his report as
accurate as possible.

Directions for Scoring.

1. Allow full value or nothing for each item.

2. Practice in any item does not mean that there can never be an
exception. For instance, if a boy or girl is kept up one night a week
beyond his regular, hour of retiring to attend a moving picture show,
nothing should be allowed for the first item under regularity. On
the other hand, should there be an imperative reason for keeping him
up later than the regular hour on an occasion of special nature, he
may receive full credit. But if such occasions occur often or regu-
larly, he should be given no credit.

3. In scoring X and XI the boy or girl should be given full credit
for items with which he has had no experience. For instance, some
children would have no incentive to play on railroad tracks, because
there would be none in their vicinity.

4. Add the scores and compare with the maximum of 500.

SCALE FOR MEASURING INDIVIDUAL AND SOCIAL BEHAVIOR
— HABITS AND PRACTICES IN ACCIDENT PREVENTION
AND HEALTH

I. Food
Variety

Drink from a pint to a quart of milk every day 3

Eat bread and butter every meal 5

Eat some fruit every day (fresh, dried, or preserved) .... 5

536

APPENDIX

Eat some green, leafy vegetable every day (spinach, lettuce,

kale, etc.) 5

Eat some starchy vegetable every day (as potato) 3

Eat a cooked cereal for breakfast daily 2

Eat meats but once daily » 2

Eat candies, cakes, etc., only as dessert 4

Quantity — Check with results determined in personal dietary work 20
Food Requirements in Calories — Age — Sex

Boys

Girls

Age

Total Cal.

Protein Cal.

Energy Cal.

Total Cal.

Protein Cal.

Energy Cal.

12-13
13-14
14-15
15-16

2300-2700
2500-2900
2600-3100
2700-3300

276-324
300-348
312-372
324-396

2024-2376
2200-2552
2288-2728
2376-3204

1850-2150
1950-2250
2050-2350
2150-2450

222-258
234-270
246-282
258-294

1628-1892
1716-1980
1804-2068
1892-2156

Regularity

Eat a warm breakfast every morning 2

Eat something warm for lunch (as soup) 3

Eat meals every day at the regular hour and in regular amounts . 3

Do not eat candies, cakes, ice-cream, etc., between meals . . 3
If hungry eat some bread and butter. Do not eat within two

hours of another meal 3

Manner of eating

Eat slowly in a calm, unexcited frame of mind '. 5

Chew all foods thoroughly 5

Engage in pleasant conversation with the family 5

Tell a story or anecdote or interesting incident of the day . . 5

II. Am

Breathing

Breathe deeply — take ten deep breaths before open window

night and morning 4

Breathe always through the nostrils, not tnrough the mouth , 5

APPENDIX 537

Bedroom air

Sleep with windows well open every night . 5

Do not sleep in draft — use window boards if necessary . . 3

Air bedroom every day 4

Schoolroom and study room

See that room where you live or study is properly supplied with
fresh air 5

Time in open air
Spend from two to three hours daily in exercise in the open air . 4

Do Not Smoke 10

III. Drink
Amount

Drink four to six glasses of water every day 2

Regularity

Drink a glass of water on rising in the morning 1

Drink two glasses of water every forenoon at regular times . 1

Drink two glasses of water every afternoon at regular times . 1

Sanitation

Do not drink out of a cup used by some one else 5

Drink only pure water from the fountain or out of a clean cup 4

Do not drink cold water while overheated from play or work . 3

Do not drink water containing cracked ice 2

Tea and coffee
Do not drink tea or coffee 9

IV. Exercise
Variety

Two hours of out-door exercise daily. Run, skate, hike, swim,
or play tennis, baseball, basket ball, volley ball, hockey, or

any other game. 20

Only light exercise should be taken one half hour before each
meal or one. hour after each meal 10

WH. FITZ. — AD. BIO. — 35 •

538 APPENDIX

V. Relaxation and Rest

Amount of Sleep 15

Sleep needed (Sleep alone)

•

Hours

13 years

14 years

15 years

8|-10
8J-10
8i-9i

16 years

17 years

18 years . . . . . .

SJ-9
8|-9
8J-9

Regularity of sleep

Go to bed at same hour every night 5

Get up at same hour every morning 5

Manner of sleep

Sleep on the side, mainly the right side 3

Relaxation

Use small pillow .... 1

Cultivate a hobby that will be of lasting benefit 10

Read good books and magazines regularly 5

Be punctual to all engagements 5

VI. Posture

Sitting

Sit erect while conversing v . ..... . 3

Sit erect while studying and writing 3

Standing

Stand erect with chest forward, head high 3

Walking
Walk with erect carriage, feet pointing directly forward ... 3
Carry books in hands, with arms straight 1

VII. Cleanliness
Hands and nails

Wash hands before each meal 10

Clean finger nails once every day 5

Keep hands and nails clean and cuticle pushed back at all times 9

Keep nails out of mouth — do not bite the nails 5

APPENDIX 539

Teeth, mouth, head
Clean teeth, mouth, and tongue morning and night .... 5

Do not put fingers, pencils, etc., in the mouth ^3

Do not dampen fingers in the mouth to turn pages of a book . 3
Do not lick postage stamps or envelopes . 3

Bathing

Take a tub bath twice every week ! 10

Take a morning shower 5

Always use an individual towel 5

Bowel movement

Have a bowel movement regularly every day 10

Do not take drugs or medicine for this. Depend solely on food,
water, exercise, and habit 10

VIII. Clothing
Cleanliness

Keep clothing well dusted and properly cleaned 5

Keep dresses and hose properly mended 4

Wear clean hose every day 4

Suitability

Wear warm, porous clothing in winter 3

Wear light, porous clothing in summer 3

Wear shoes with broad heels, and of sufficient length .... 4

Miscellaneous

Put on a wrap when sitting down after exercises 3

Keep clothing properly aired . 3

Do not sleep in clothing worn during the day 5

Always have a clean handkerchief 3

IX. Home Study
Regularity

In general, study at the same time each day, preferably early
evening •■ 2

540 APPENDIX

Light
Use a steady and sufficient artificial light. Avoid a glaring
light 1

Quiet

Have a quiet room for study. Avoid family conversations,
radio, etc 4

System
Avoid movies and parties during the school week 2

X. Safety Habits
In the streets

Look in both directions before crossing the streets 3

Go straight across the street and at the crossings only ... 3

Do not tarry in the street but cross promptly 3

Help younger children to cross the street safely 3

Do not play on railroad tracks 3

Do not handle dangling wires or come in contact with electric

wires 5

Do not ride on the outside of street cars 3

Do not beg rides on autos 5

Do not climb on trucks and wagons 3

At home

Be careful about the use of matches ; keep them in a safe place 2
Be careful about the use of kerosene and other inflammable
materials ; keep them in a safe place ; do not start a fire with

them 2

Be careful always in using the gas range 3

Be sure electric wires are disconnected before touching them . 3

Be careful about the stairways and fire escapes 3

Do not climb on chairs, tables, and step-ladders unless neces-
sary, and then only after examining them 3

Do not place heavy objects or sharp instruments where they

may fall upon some one • 3

Do not leave chairs or other objects where some one may
stumble over them in the dark 3

APPENDIX 541

Do not start your automobile engine in a closed garage ... 3
Have an annual health examination and have remediable defects

corrected ? 10

Visit the dentist every six months 5

At school

Do not hurry down the stairways 3

Do not run in the halls 3

Look before going in and out of doors, and do not rush ... 3

Take one step at a time on stairways 3

At play

Do not run on busy traffic streets in play 3

Do not play near high places or on rough grounds .... 3

XI. Service — Social and Civic Habits and Practices

Service at home

Give some help to your mother or father every day .... 5

Keep shoes shined, clothes brushed 5

Go on errands cheerfully 5

Service at school

Serve on Health or Safety Committees 5

Call attention in every case to children who violate health or

safety practices . ...... 5

Service to the community

Notify the Police Department of any obvious violations of

ordinances 3

Notify the Fire Department in case of fire 3

Notify the Health Department of menaces to health in the

neighborhood 5

Notify the Street Department of holes in the street, obstruc-
tions, unclean alley in neighborhood, etc 3

o W

<*>

3£

S&'S

>©

o»

«-<

""■

%■*

«*

*-4

-* .

38
39

34
35

34*

WEIGHT-HEIGHT

36*

38*

42
43

39
41

39*
41*

AGE TABLE

42
43

44*

BOYS

45
46

46
47*

46
48

46*
48

46*

48*

45
46

49*

50*

53
55

52
55

53
55

53*
55

55*

57*

58*

61*

64*

66*

68*

72*

74*

75*

80*

79 *

83*

91*

100

103

106*

104

100*

101

102

103

104

107

111

116*

111

105*

106

107

108

113

118

123

127

' 63

117

109

111

113

115

117

121

126

130

* 64

123

114*

117

118

120

122

127

131

134

129

119

122

125

128

132

136

139

133

124*

128

130

134

136

139

14>

■ 67

139

134

137

141

143

147

144

137

139

143

146

149

152

147

143

144

145

148

151

155

152

148*

150

151

152

154

159

157

153

155

156

158

163

157*

160

162

164

167

169

160*

164

168

170

171

Age — years

Average (Shorl

height jMedi

urn

(inches) iTall

Average [Sho

annual {Met

lium

gain (lbs.) ITall

Baldwin, B. T., and Wood, T. D., Weight-Height-Age Tables. American Child Health
Association, New York, N. Y.

542

III

>*
00

33
34

38
39

WEIGHT-HEIGHT

36*

Si'

42
43

39
41

39*
41

41*

AOE TABLE

42
43

42*

45
46

45
47*

45
47

45
48

45*
48*

GIRLS

45
45

49*

50*

52
55

52
54

52
55

53*
56

si*

56*

62*

63*

66*

71*

73*

72*

78*

83*

80*

92*

96*

101*

100

103*

104*

101

91*

101

105

108

109

111*

108

100

101

105

108

112

113

116

114

104*

105

106

109

113

115

117

118

110

112

116

117

119

120

121

114*

115

117

119

120

122

123

125

118*

120

121

122

123

125

126

129

124

125

128

129

130

133

128*

130

131

133

135

138

131*

133

135

136

138

142

135*

137*

138*

140*

142*

144

136*

138*

140*

142*

144*

14S

138*

140*

142*

144*

145*

Age- Years

Average (Shoi

Height {Mec

(inches) [Tall

Average fSho

Annual { Mec

lum

Gain (lbs.) ITaU

Baldwin, B. T., and Wood, T. D., Weight-Height- Age Tables. American Child Health
Association, New York, N. Y.

543

544 APPENDIX

A SUGGESTED COURSE OF STUDY IN ADVANCED

BIOLOGY

(Now being tried in 30 schools)

TERM I
I. Cell Studies

1. Study of the living green cell ; illustrated in Spirogyra or Elodea.

(a) Structure ; microscopic study.

(b) Functions ; emphasis on food-manufacture.

2. Study of the living animal cell ; illustrated in amoeba or Para-

mecium,
(a) Structure ; microscopic study.
(6) Functions.

(d) Comparison of plant and animal cells as to structure and
functions.

3. Study of the typical or generalized cell.
(a) Structure.

(6) Comparison and nature of protoplasm.

4. Cell division,
(a) Amitosis.

(6) Mitosis ; names of phases optional.

5. Association of cells in tissues and organs.

(a) Study of human tissues ; four of the following required :

epithelial, muscle, bone, connective, nerve.
(6) Differentiation, specialization, physiological division of

labor,
(c) Comparison of tissue cell with independent plant or animal

cell.

6. History of cell theory ; contributions of any three of the follow-^
ing : Hooke, Malpighi, Leeuwenhoek, Schleiden, Schwann, Max
Schultze.

APPENDIX 545

II. Nutrition

1. (Optional) Study of the frog as an introduction to human

nutrition,
(a) Identification of systems of organs.
(6) Appearance and location of organs.

2. Study of metabolism in man.

(a) Digestion.

1. Purpose.

2. Foods; uses of different nutrients; include vitamins
and deficiency diseases ; omit planning of diets and food
tests.

3. Alimentary canal and digestive glands.

4. Enzymes, intermediate products, end products.

5. Experiments showing digestion.

6. Peristalsis.

7. Hygiene of digestion.

(b) Absorption.

1. Purpose.

2. Adaptations.

1. Purpose.

2. Composition of blood ; function of each part ; clotting.

3. Organs of circulatory system.

4. Course of blood; changes in composition in various
organs.

5. Lymph and lymphatic system.

6. Hygiene of circulation.

7. Discoveries of Harvey, Malpighi, and Leeuwenhoek on
the blood and circulation.

(d) Assimilation.

(e) Respiration.

1. Brief study of air passages.

2. Emphasize cell respiration.

(f) Secretion.
1. Duct glands.

• <

546 APPENDIX

2. Endocrine glands and hormones; secretin, pancreatic
hormone; secretions of thyroid, adrenal, and pituitary
glands.
(g) Excretion.

1. Formation of principal waste products; carbon dioxide,
water, urea, uric acid.

2. Organs of excretion.

3. Hygiene of excretion.

(h) Summary of metabolism of carbohydrates, fats, and proteins.

3. Parasitism, saprophytism, and symbiosis.

(a) Definitions and examples; omit all detailed study, except
as included under bacteria and malarial parasite.

(6) Life history and importance to mankind of one parasite ;
malarial organism suggested.

4. Comparative study of different types of nutrition.

III. Irritability

1. A function of protoplasm; illustrated in protozoa.

2. Tropisms in plants ; geotropism, hydrotropism, phototropism ;
demonstrate, unless covered in elementary biology.

3. Irritability in man.

(a) General structure and functions of the nervous system;
emphasis on function.

1. Central nervous system.

a. Brain; including cerebrum, cerebellum, medulla,

and their general functions.
6. Spinal cord and its general functions,
c. Nerves, cranial and spinal ; omit names of individual

nerves.

2. Autonomic system.

3. Neurons, cranial and spinal ; omit names of individual
nerves.

(6) The types of nervous reactions.

1. Inborn automatic activities; reflex actions and the
reflex arc.

APPENDIX 549

3. Bacteria as useful organisms,
(a) In food preparation.

1. Ripening and flavoring of dairy products.

2. Making of vinegar.
(6) In agriculture.

1. Decay.

2. Nitrification ; comparison with dentrification.

3. Nitrogen ; fixation. Nitrogen cycle.

4. Rotation of crops.

1. Retting of flax.

2. Tanning of leather.

4. Bacteria as harmful organisms.

(a) In decay of foods (optional) ; methods of food preservation.
(6) In causing disease.

5. Pathogenic microorganisms ; study of the following diseases :
diphtheria, tuberculosis, colds, typhoid fever, smallpox, tetanus,
hydrophobia, malaria, yellow fever, focal infections ; to bring out
the following principles :

(a) Sources of infection ; contact, food, and drink, air, human

carriers, insect carriers.
(6) Bacterial poisons ; toxins, ptomaines.

(c) Methods of protections; skin, adaptations of respiratory
tract, white corpuscles. Antibodies (antitoxins, lysins,
agglutinins, and opsonnis).

(d) Methods of immunity and immunization.

1. Active; vaccination, toxin-antitoxin innoculation ;
Pasteur treatment.

2. Passive; antitoxin treatment.

3. Tests for immunity ; Schick test.

(e) Description of the causative organism, general character
of disease, symptoms, diagnosis, prevention, and treatment
(where discussion is feasible) for each of the diseases.

(/) Work of the Department of Health.

(g) Biography; scientific contributions of Jenner, Lister, Pas-
teur, Koch, Metchnikoff, Ehrlich,

INDEX

Ability, families of inferior, 358-362;
families of superior, 356-358

Abrasion, meaning of, 168

Absorption, digestion and, 125-141 ;
from large intestine, 138 ; from small
intestine, 136-138 ; in organism, 34 ;
in green cell, 34-36; stomach, 136

Acidopholus milk, 140

Acne, definition of, 175

Acquired reactions, 220-221

Acromegaly, 197

Active immunity, acquiring, 507-508

Activities, acquired automatic, 220-221 ;
inborn automatic, 215-217 ; kind of
mental, 215; reflex, 215-216; volun-
tary, 219-220. See also Nervous
activities

Adam's apple, 179

Adaptability, relation to health, 414-415

Adaptations, of tissues, 88-89 ; of higher
plants, 69-72

Adaptive processes, in organisms, pur-
pose of, 34

Addison's disease, causes of, 198-199 ;
characteristics of, 198

Adenoids, 179-180 ; colds result of, 475-
476

Adipose tissue, use of, 81-82

Adolescence, table of, 302

Adrenal glands, effect of secretion on
body, 197-198; location of, 197;
relation to arterial pressure, 197-198.
See Addison's disease

Adrenaline, 197 ; use of, 199

Adrenin, effect on body, 197-198

Afferent axon, 209

Agar slant, inoculation of, 398 ; prepara-
tion of, 396-397

Age, chronological, 229; mental, 228;

. of earth, 378, 381 ; of science, 1-3

Agglutination test, 465-466, 467

Agglutinins, 465, 467, 469; in typhoid,
467 ; production of, 501 ; to determine
presence of, 465-466 ; use of, 501

Agriculture, bacteria in, 405-411

Air, composition of expired, 183 ; com-
position of inspired, 183 ; tidal, 183

Air sacs, 179

Air tubes, 179-180

Alcohol, effect on circulation, 168-169 ;
effect on nervous system, 237

Algae, characteristics of, 33 ; classified,

519
Alimentary canal, laboratory study of,

in frog, 116; in man, 117; description

of man's, 118, 119-120
Alkali, laboratory problem, effect on a

fat, 131-132
Allosaurus, prehistoric reptile, descrip-
tion of, 383 ; restoration of, 372
Alveolar theory, of nature of protoplasm,

54
Amitosis, meaning of, 60 ; process of, 60
Amoeba, assimilation in, 44 ; behavior of,

44 ; digestion of, 43 ; ingestion of, 43 ;

irritability of, 44-46 ; laboratory

problem on study of, 42-43 ; life

functions of, 43 ; locomotion of, 46 ;

regeneration of, 56 ; reproduction of,

44, 248 ; respiration of, 44
Amphibia, 525-526
Amylase, an enzyme, 38, 131 ; amylopin,

131
Anabolism, in cell, activities in, 60;

meaning of, 59, 187
Anaemia, causes, 146, 167 ; symptoms,

147
Anaphase, stage in cell division, 61, 62
Ancestry, influence in development, 310-

313
Andalusian fowls, heredity in, 318-320
Andrews, Roy Chapman, on Mongolian

expeditions, 385-387. See frontispiece
Angiospermae, meaning of, 520, classi-
fied, 520
Animal, and plant breeding, 343-354
Animal cell, typical, 42-52
Animal passage, meaning of, 508
Annelida, classified, 522-523 ; meaning

of, 522
Anopheles, spread of malaria by, 482-484
Ant eater, giant, 512
Anthozoa, 522
Antibodies, agglutinins, 501 ; antitoxin,

501 ; lysins, 501 ; opsonins, 500, 502 ;

precipitins, 501-502 ; production of,

146, 501 ; use of, 146
Antiseptics, laboratory problem to show

effect on growth of bacteria, 401-402 ;

use of, 4
Antitoxin, discovery of diphtheria, 451-

452 ; kinds of, 501 ; preparation of

551

552

INDEX

diphtheria, 451-452, 456 ; preparation
of tetanus, 461 ; produced in body,
501 ; scarlet fever, 459 ; standardizing,
456 ; use of, 501

Aorta, 153, 159

Aphids, 271

Appendicitis, 135

Appendix, vermiform, 135

Arachnida, 524

Archaeopteryx, earliest known bird, 383

Archiannelida, 523

Aristotle, classification by, 510 ; Father
of Biology, 10 ; idea of evolution, 371 ;
work of, 11

Arterial blood, 144

Arteries, direction of flow of blood in,
154, 156; functions of, 154, 156;
hardening of, 168 ; meaning of name,
153, 156; regulation of size of, 156;
"rupture of, 168; structure of walls of,
156

Arterioles, 159

Arteriosclerosis, causes of, 168

Artery, pulmonary, 153

Arthropoda, classified, 517; 523-524;
meaning of, 523

Artificial selection, importance in animals
and plants, 352

Ascaris, diagram of mitosis of egg of, 61

Asexual reproduction, by vegetative
propagation, 255-263 ; of algae, 247-
248 ; of bacteria, 247 ; of hydra, 248,
249-250 ; of protozoans, 248 ; of yeast,
250-251

Assimilation, a life process, in amoeba,
44 ; in green plants, 39-40

Asteroidea, 522

Asthma, cause of, 477; treatment of,
477 ; vaccination for, 477

Auricles, of heart. See Heart

Autonomic nervous system, description,
210 ; diagram of, 210 ; functions of,
210-211 ; importance in nervous
activities, 221-222 ; relation to cen-
tral nervous system, 210-211

Aves, animals of class, 526

Axon, of nerve cell, 86, 87

Bacilli, form of bacteria, 392

Bacillus, acidopholus, 140; bulgaricus,
140 ; typhoid, 465

Bacteria, 391-411; action on body,
494-495 ; aerobic, 393 ; anaerobic,
393; beneficial activities, 403-411;
cause of pus, 494 ; cause of disease, 494-
495 ; carried through lymphatics, 500 ;
colony of, 395 ; conditions necessary
for growth, 399-400 ; cultures of, 396-
397, 398 ; denitrifying, 407 ; destruc-
tion of white corpuscles by, 500,
504-505; effect of temperature on,

399, 499; forms of, 392-393; func-
tions of, 393-395 ; growth in milk,
140; growth of, 398-399; in agri-
culture, 405-411 ; in our body, 494-
500; in air, 495-496; 475; in dust,
473 ; in eyes, 496 ; in food preparation,
403-404, 405 ; in industries, 403-404 ;
in lymph and lymph nodes, 166-167,
500 ; laboratory problem to determine
bacterial content of milk, 401 ; labora-
tory problem to determine number of
bacteria in air, 400-401 ; laboratory
problem to show effect of antiseptics
on growth of, 401-402 ; media for
cultivation, 396-397; methods of
entering, body, 495-496; methods of
identifying, 395-396 ; nitrifying, 406 ;
nitrogen-fixing, 394, 407-409; nutri-
tion of, 394 ; occurrence of, 397-399 ;
of decay, 406 ; parasitic, 393 ; patho-
genic, 394 ; physiological functions of,
393-395 ; relation to disease, 494-495 ;
saprophytic, 391, 394; soil, 405-411;
structure of, 391-393

Bacterial content, laboratory problem, in
air in various places, 400 ; in milk, 401

Bacteriolysin, antibody, 501 ; function
of, 465, 469

Bacteriology, definition of, 17

Bacteriophage, 508

Banting, F. G., work with insulin, 199

Beach plum, improved, 348-349, 352, 353

Beetle, potato, effect of environmental
conditions on, 341

Behring. See Von Behring

Beriberi, cause of, 98-99, 100; preven-
tion of, 99, 100

Bile, basis for manufacture of, 161 ;
function of, 132

Binet, Alfred, tests by, 228

Binet scale, 228

Binet-Simon Scale, Terman's revision,
228

Binomial system, of classification, 510-
511

Biogenetic law, 388-389

Biology, affected by work in other
sciences, 19 ; divisions of, 17 ; mean-
ing of, 15 ; of to-morrow, 1-9 ; pur-
pose of, 6-7 ; relation to chemistry, 16 ;
relation to health, 7-8; relation to
other sciences, 16 ; relation to physics,
15-16 ; relation to vocations, 8-9

Birds, egg-laying of, 299 ; food of, 299 ;
nest-building of, 298 ; infancy among,
298-299 ; reproduction of, 288-289

Bishop, on vitamin E, 103-104

Blackberry, production of white, 347-
348, 349

Bladder, urinary, function of, 175-176 ;
structure of, 175

INDEX

553

Blastula, 286

Bleeders. See Haemophilia

Blood, arterial, 144 ; a tissue, 87, 146 ;
circulation of, 143, 153-161 ; clotting
of, 148 ; composition of, 145 ; corpuscles
of, 87-88, 147-148 ; count, 147 ; course
of, 159-161 ; early drawing of circula-
tion of, 151 ; functions of, 145-146,

150, 162 ; grouping of, 148-149 ; heat
of, 150 ; importance of, 143-150 ; lab-
oratory problems on study of, 87,
143-144 ; laboratory study of cor-
puscles of, 144-145 ; laboratory study
of serum of, 144 ; necessity of circu-
lation of, 149-150 ; need of water to,
167 ; of frog, 89 ; of man, 88 ; oxygen-
ated in lungs, 179 ; properties of, 145-
146 ; serum of, 144 ; transfusion of,
149 ; venous, 144

Blood plasma, composition of, 145
Blood platelets, function of, 148 ; struc-
ture of, 148
Blood serum, laboratory study of, 144
Blood vessels, 143 ; laboratory study of,

151. See also Arteries, Capillaries,
and Veins

Bone, formation of, 79 ; laboratory
problems on microscopic structure of,
78; laboratory study of cross struc-
ture of, 77-78 ; proper growth of, 80

Bone cell, diagram of, 80

Brain, parts of, 206-207; structure of,
206-207

Breathing, control by carbon dioxide,
183 ; control by oxygen, 183 ; labora-
tory problem of modifications of, 183 ;
laboratory problem on mechanics of,
181 ; movements of, 181-182

Breeding, aims of, 345-351 ; artificial
selection in, 352 ; for improved quality,
350 ; for increased production, 351 ;
for points, 349-350; hybridization,
351 ; importance of animal, 344-345 ;
353 ; importance of plant, 343-345 ;
Mendel's experiments in, 322 ; methods
of animal, 353-354 ; methods of plant
propagation in, 351-353 ; results of
close, 353-354

Breeding experiments, of plants, by
Mendel, 322

Bronchi, 178, 179

Bronchial tubes, 179

Bronchitis, 474

Broncho-pneumonia, predisposing fac-
tors, 474

Brontosaurus, restoration of, 372. See
Dinosaur

Brown, Robert, described movement of
molecules, 35-36 ; observed nucleus of
cells, 27-28

Brownian motion, 36

WH. FITZ. AD. BIO. — 36

Bruise, cause of, 168

Bryophyta, 519

Budding, laboratory problem in yeast
cells, 248-249 ; method of reproduc-
tion, 248-250; of hydra, 249-250;
of sponges, 253

Bulbs, propagation by, 262-263

Burbank, Luther, experimental methods
of, 14 ; fruit improved by, 347-349 ;
on potato blight, 344

Calcarea, 521

Calcium, need for, 111

Calkins, Dr., experiments on regenera-
tion, 56

Calorie, defined, 93 ; needs, 105

Calorimeter, measurement of human
energy by, 189

Calyx, of flower, function of, 274

Canning, 400

Capillaries, broken, 168; function of,
157 ; in lungs, 179 ; pressure in, 157 ;
structure of, 157

Carbohydrates, manufacture of, 36-37 ;
metabolism of, 188; constituents of,
36-37

Carbon cycle, 409

Cardiac opening. See Stomach, parts of

Carnivora, animals of Order, 527

Carrell, Alexis, cultivation of cells, 54-
55 ; preparation of Dakin solution, 55

Cartilage, functions of, 79-80 ; kinds, 79

Catalytic agents, in digestion, 38

Catarrh, cause of, 474

Cebidae, 527

Cell, absorption in green, 34-35 ; amitosis
in, 60 ; assimilation in, 39-40 ; cultiva-
tion of, 54-55 ; digestion in green, 38 ;
direct division of, 41, 60; discovery
of nucleus of, 27-28 ; division of, 41 ;
excretion in green, 40 ; food manufac-
ture of studies of, 36-38; functions
of green, 34^0; history of, 27-33;
growth and division, 40, 41, 53-64;
inclusions in, 37 ; indirect division of,
60-63 ; irritability in green, 40-41 ;
key to all biological problems, 29-30;
laboratory study of Elodea, 28-29;
laboratory study of onion, 25-26;
laboratory study of narcissus leaf, 30-
31; laboratory study of Spirogyra,
31-33 ; mitosis of, 60-63 ; named and
described by Hooke, 27-28; nature
and composition of, 53-55 ; primary,
269, 285; relation to heredity, 55;
respiration in green, 38-39 ; resting
and dividing, 53-64 ; sex, 269 ; somatic,
269 ; structure of, 30 ; theory, 28, 30,
52, 64 ; typical animal, 42-52 ; unit of
function of organism, 30; unit of
structure of organism, 30, 53 ; 73 ;

554

INDEX

57-58; wall of, 52, 58; work of all,
162

Cellulose, of plant cells, 52

Central nervous system, divisions of,
205; functions of, 206-210; protec-
tion of, 205-206

Centrosome, function of, 59 ; in cell
division, 61-62

Cephalopoda, 523

Cercopithecidae, 527

Cerebellum, function of, 207; level of
reaction in, 218, 219, 220 ; nature of,
207

Cerebro-spinal nervous system. See
Central nervous system

Cerebrum, function of, 206-207; level
of reaction in, 218, 220; nature of,
206 ; position of, 207 ; size in various
animals, 207 ; structure of, 206

Cetacea, animals of Order, 527

Chaetopoda, 523

Chambers, Prof. R. H., dissections under

• microscope by, 23, 45 ; on heredity, 55

Chance, law of, laboratory problem to
demonstrate, 317

Character, dominant, 324, 333; of off-
spring, 306-317 ; recessive, 325, 333

Character-determiners, in chromosomes,
55, 319

Characters, acquired, 336-337 ; domi-
nant, 324, 333; inherited, 336; 318-
333 ; law of unit, 327-333 ; recessive,
325, 333; secondary sexual, 281-282

Chemistry, and its relation to biology, 16

Chemotropism, shown by amoeba, 46.
See Tropisms

Chicken pox, effects of, 478 ; method of
spread, 478

Child-labor laws and eugenics, 366-367

Chiroptera, animals of Order, 527

Chlorophyll, in plants, function of, 36-37,
39, 59

Chloroplasts, first seen, 28 ; function of,
59 ; structure of, 28

Chordata, classified, 525-527 ; meaning
of, 525

Chromatin granules, function of, 57 ;
structure of, 55

Chromosome, changes in number, 339 ;
number in sex cells, 270-271

Chromosome theory, of inheritance, 331-
333

Chromosomes, 55 ; behavior in cell
division, 62 ; behavior in maturation,
268-269, 284, 316 ; continuity of, 306,
307 ; laboratory problem to show
chance combinations of genes in, 317 ;
laboratory problem to show possible
combination of genes in, 326-327 ; lo-
cation of genes in fruit fly, 312 ; locus
of genes, 331 ; number in sex cells and

body cells of various animals, 307;
270-271; relation to heredity, 315-
317, 324-326, 331-333

Chronological age, 229

Chyme, 129

Cilia, in Paramecium, 48, 49, 50; in
respiratory tract, 75, 179

Circulation, of blood, 143 ; coronary,
154 ; early investigations of the., 163-
165 ; effect of violent emotions on,
167 ; necessity of, 149-150 ; organs of,
153-154 ; portal, 160-161 ; pulmo-
nary, 160; systemic, 159-160; time
for complete, 161. See Blood

Circulatory system, 151-162 ; diagram
of, 155 ; functions of, 168 ; hygiene of,
167-169

Classification, basis of, 512-514 ; diffi-
culties in, 511-514 ; evolution in, 517-
518; geographical distribution and,
573; habits and, 513-514; Interna-
tional Commission on, 514-515; mor-
phology in, 513 ; of plants and animals,
518-527 ; present method of, 515-518

Cloaca, in frog, 115

Close-breeding, reasons for and results
of, 353-354

Clotting of blood, 148

Cocci, form of bacteria, 392

Coelenterata, classified, 521-522 ; mean-
ing of, 521

Cohnheim, J., experiment on transmis-
sion of tuberculosis, 438

Cold, a common disease, causes of, 473-
475 ; chronic, 474 ; effects on body,
473-474 ; predisposing factors, 474 ;
prevention of, 475-476 ; remedial meas-
ures, 476 ; transmission of, 474-475

Collip, experiment with parathyroid ex-
tracts, 196

Conjugation, 264; of Paramecium, 49-
50, 267-268

Connective tissue, 81-82

Conservation, of soil, 411

Constipation, causes of, 139 ; prevention
of, 139, 140

Continuity, of germ plasm, 336

Contractile tissue, 83

Contractile vacuole, of amoeba, 42 ; ot
Paramecium, 47

Corolla, of flower, function of, 274

Coronary circulation, 154

Corpuscles, white, description of, 88;
functions of, 88, 147-148 ; in infec-
tion, 148; number of, 88, 147; red,
destruction of, 146 ; formation of,
146 ; function of, 88, 146 ; number of,
88, 147 ; size of, 88 ; structure of, 88

Cortex, of brain, areas of, 206-207, 213 ;
functions of, 207, 213 ; structure of, 206

Cotyledons, 278-279

INDEX

555

Cowpox, inoculations with, 421-423
Cows, increased products from, 344
Cretinism, 194
Cretins, cause of, 194
Criminals, heredity of, 361
Crinoidea, 522
Crops, rotation of, 409-411
Crossing-over, of genes, 339, 340-341
Crustacean, 524 ; the young of, 296
Culex, house mosquito, 483
Cuts, treatment of, 168
Cuttings, method £>f vegetative propaga-
tion, 255-256
Cyclostomata, animals of Order, 524
Cytoplasm, 58 ; structures found in, 57
Cyton, of nerve, 208, 209

Dakin solution, 55

Darwin, Charles, 371 ; on natural selec-
tion, 373-376

Darwinian theory, of evolution, 373-
376

Darwin's, theory of, evolution, 373-376 ;
over-production, 374 ; struggle for
existence, 374 ; variations, 374-376 ;
survival of the fittest, 374 ; inherit-
ance, 374-375

Davenport, Charles, 355 ; work in eu-
genics, 356

da Vinci, Leonardo, 163-164; on fossils,
371

Defecation, 135

Demospongia, animals of class, 521

Dendrites, 86-87 ; axon, 208

Dentine, 107

Dentrification, process of, in soil, 407

Dermis, structure of, 172

Development, progressive. See Organic
evolution

Development, influenced by ancestry,
310-313 ; influenced by environment,
313-315

Development of species, use and disuse,
372

de Vries, Hugo, experiments with eve-
ning primroses, 337 ; mutation theory
of, 376-377; portrait of , 335 ; theory of
evolution, 376-377 ; mutants, 376-377,
338-339

d'Herelle, on immunity, 508-509

Diabetes, insulin in treatment of, 199

Dick test, for scarlet fever, 458

Diet, complete, 93 ; essential, 104 ; in-
sufficient, 93 ; insufficient in min-
erals, 95-96 ; insufficient in proteins,
93, 95 ; investigation by McCollum on,
93, 95 ; laboratory problem on per-
sonal, 105; relation of teeth to, 111—
112

Digestion, and absorption, 125-141 ;
chart of chemical, 134; hygiene of,

138-139; in mouth, 120-121; in
plants, 38 ; in small intestines, 132-
133, 135 ; laboratory problem of rela-
tion of size of protein food to time of,
126 ; laboratory problem of relation of
different animal proteins to, 127 ; life
function of amoeba, 43 ; meaning of,
117-118; process of, 117-119; sali-
vary, 121-122, 130; time necessary
for, 133, 140

Digestive organs, of frog, 114-116, 117;
of man, 116-117, 119

Digestive system, 114-123; function of,
117; laboratory study of the frog's,
114-116; laboratory study of man's,
117

Dinosaur, amphibian, 383 ; eggs of,
306 ; restoration of, 372

Diphtheria, ages most susceptible to, 453 ;
causes of, 453-454; diagnosis, 457;
discovery of active immunity to, 452-.
453 ; discovery of antitoxin of, 451-
452 ; effect on the body, 454 ; history
of, 450 ; isolation of organism of,
450 ; isolation of toxin of, 451 ; pre-
vention of, 457-458 ; Shick test of
susceptibility, 453 ; transmission of,
454-455 ; treatment of, 455-457

Disease, and health, 413-414 ; and men-
tal poise, 502-503 ; causes of, 494 ;
due to bacteria, 445, 455, 459, 482,
492 ; due to physical agents, 473 ; im-
munity of animals to, 345 ; immunity
of plants to, 347 ; inheritance of, 368-
369 ; safeguards of the body against,
496-503 ; caused by toxin, 450-451, 458

Division, cell, process of, 41 ; purpose of,
40

Division of labor, physiological, 66-67

Division, reduction. See Maturation

Dominance, complete, 323-324 ; incom-
plete, 318-321; meaning of, 323;
Mendel's or Mendelian law of, 322-324

Dominant characters, 323-324; list of,
333

Dogs, developed from common ancestor,
310, 311

Duck bill, 384, 513

Duct, thoracic, 165

Ductless glands, 191-201 ; adrenal, 197-
199 ; pancreas, 199 ; parathyroid, 196 ;
pineal, 200; pituitary, 196-197; re-
productive, 200-201 ; secretions of,
191-192 ; spleen, 200 ; thymus, 199-
200 ; thyroid, 192-195

Dujardin, protoplasm named by, 28

Dwarfism, 197

Earth, age of, basis for estimate of, 378-
381 ; calculations of, 378 ; evidences
of, 378-379, 380

556

INDEX

Echinodermata, classified, 522 ; mean-
ing of, 522

Echinoidea, 522

Ectoderm, development of, 286 ; of
embryo, 286 ; systems formed from, 286

Edentata, 526 ; ant eater, 512

Education, and eugenics, 365 ; health an
objective of, 415-417

Edwards, Jonathan, family of, 357

Effector, response activity of, 209

Egg cell, characteristics of, 268

Eggs, differ from seeds, 281 -, of insects,
281 ; of birds, 281 ; production by
frog, 284-285

Ehrlich, portrait, 504; theory of im-
munity, 505-506 ; work of, 14

Elasmobranchii, animals of Order, 524

Elastic tissue, use of, 81

Elodea, diagram of, 30; laboratory
study of cells of, 28-29

Embryo, development of seed, 278-279 ;
protection of, in lower animals, 295-
296; 288-289; in insects, 297-298;
in mammals, 299-301 ; in man, 301

Embryo sac, 274, 276, 277

Embryological evidence, of evolution,
388-389 ; similarities in development of
embryos of vertebrate animals, 388-389

Emotions, dangers of violent, 167

Enamel, of teeth, 107

Encystment, of protozoans, meaning of,
253 ; why formed, 253

Endocrine glands, 191

Endoderm, of embryo, 286

End-organs, in skin, functions of, 173

Endosperm, 278, 279; in grains, 279;
systems formed from, in embryo,
286

Endotoxins, meaning of, 495; of tuber-
culosis, 442 ; of typhoid, 465-466

Energy, human, measured by calorim-
eter, 189 ; kinetic in plant cells, 39

Enterokinase, use in digestion, 133

Environment,' effect on ancestral traits,
313-315 ; influence on development of
animals, 308-310; influence on de-
velopment of plants, 308, 309 ; meth-
ods of improving, 364-367 ; versus
heredity, 369-370

Evironments, effect of different, 308

Enzymes, digestive action of, 128, 131 ;
function in plants, 71 ; in gastric juice,
128 ; in intestine, 132-133 ; in plant
cells, 38 ; in saliva, 121 ; of pancreatic
juice, 131 ; specific action of, 128-129,
131

Epidermis, laboratory problems on
study of leaf, 30-31, 67; laboratory
problem on cross section of leaf, 67-
68; outer layer of skin, 171, 172

Epiglottis, use of, 122

Epithelial cells, laboratory problem on
75 ; shape of, 75

Epithelium, 75-77

Erepsin, 132

Esophagus, 122, 123

Essay on Population, Malthus, 343

Eugenics, 355-370 ; child labor laws and,
366-367 ; compulsory education and,
365; immigration and, 367-368;
laborer compensation laws and, 365 ;
movement founded and named, 355 ;
need for understanding, 363 ; relation
of marriage to, 355-356; 363-364;
Second International Congress of, 355 ;
versus euthenics, 368 ; vocational
guidance and r 367 ; widows' pensions
and, 365-366

Eugenics Laboratory, at Cold Spring
Harbor, 356 ; symbols used in chart
making at, 356 ; work done by, 362-
363

Eustachian tubes, 122

Euthenics, consists of, 365-368 ; mean-
ing of, 355, 362 ; versus eugenics, 368

Evans, on vitamin E, 103-104

Evening primroses, de Vries' experiments
with mutants of, 337

Evolution, organic, Aristotle's idea of, 371 ;
Darwin's natural selection theory of,
373-376 ; de Vries' mutation theory of,
376-377 ; embryological evidences of,
388-389 ; geographical evidences of,
385-386 ; history of, 371 ; geological
evidences of, 381-384 ; in plants, 389 ;
Lamark's use and disuse theory of,
371-373 ; meaning of, 371 ; morpho-
logical evidences of, 386, 387 ; vestigial
evidences, 387-388

Evolutionists, beliefs of, 37i

Excretion, definition of, 170 ; hygiene of,
174-175, 176 ; importance of, 170 ; of
man, 170-176 ; process in a green cell,
40

Excretory organs, 170-176

Exotoxins, 495 ; in diphtheria, 451 ; in
scarlet fever, 458 ; in tetanus, 459 ;
in tuberculosis, 442

Experimentation, modern methods of, 15

Expiration, meaning of, 182; process of
in man, 182

Fi, defined, 319

F 2 , defined, 319

Families, of inferior ability; 358-362;
of superior ability, 356-358

Fatigue, cause of, 232 ; effect of, on
individual, 232-233 ; how to over-
come, 233 ; test of muscles of frog for,
230

Fats, laboratory problem of effect of
alkali on, 131-132 ; metabolism of, 190

INDEX

557

Fermentation, during reproduction of
yeast plants, 250-251

Fertilization, adaptations for, in plants,
293 ; double, 278 ; external and in-
ternal, 283, 288; in frog, 270-271,
283-284, 285; in higher plants and
animals, 268, 269 ; in plants, 277-278 ;
significance of process, 285

Fever. See Yellow fever, Typhoid

Fibrinogen, in blood, 143, 145, 148

Fibrous tissue, functions of, 80-81

Fibrovascular bundles, structure of, 70

Filament, of Spirogyra, 32

Filter passers, 393

Filterable virus, 393

Fish, care of young, 296 ; spawning of,
283-284

Fission, binary, a form of cell division,
44, 247-248

Fixation, of nitrogen, by bacteria, 407-
408

Flanders, on intelligence testing, 239-231

Flatworms. See Platyhelminthes

Flax, useless parts removed by bacteria,
405

Flowers, calyx of, 274 ; corolla of, 274 ;
essential organs of, 274 ; production of
female gamete, 276-277; production
of male gamete, 275-276

Fluid, tissue, 165

Foam theory, of nature of protoplasm, 54

Focal infection, common, 478 ; defined,
174-175, 477; effect of, 477; pre-
vention, 478

Focusing, miscroscope, rules for, 24

Folds, in small intestine, 136

Follicle, hair, 173

Food, bacteria in preparation of,* 403-
404 ; definition of, 91 ; improvement
in quantity and quality of, 344-345 ;
manufacture in green cells, 36-38 ; nu-
trients, 91-104 ; of plant cells, 36 ; pres-
ervation of, 399—100 ; storage of, 71

Food manufacture, in green cells, 36-38 ;
process of, 36-37 ; the products formed
in, 37-38

Food nutrients, 91-104; table of, 94

Foods, containing mineral, 96 ; contain-
ing proteins, 95 ; energy value of, 92 ;
fuel value of, 92 ; importance of, 91

Formation of fruit, 279

Fossils, formation of, 378, 381 ; state of
perfection, 381

Four-o'clocks, heredity of, 320-322

Freak. See Mutants

Frog, breeding habits of, 282-283 ; de-
velopment of, 285-286; laboratory
study of alimentary canal of, 116 ; lab-
oratory study of internal organs, 114-
116; life history of, 287; produced
parthcnogenetically, 271-272 ; produc-

tion of eggs, 284-285; production of
sperms, 285

Fruit, function of, 279

Fruit fly, location of genes in chromo-
somes of, 312, 332

Fuel, in plants, 37

Functions, of green cells, 34-41

Fungi, characteristics of, 33 ; classified,
518-519 ; meaning of, 33

Galen, idea of circulation, 163, 164

Galton, Sir Francis, application of statis-
tical method to study of human
heredity, 357 ; interest in eugenics,
355

Galvanotropism, shown by amoeba, 46

Gametes, female, 266; formation of,
264 ; male, 266 ; production in flower-
ing plants, 275-277

Ganglion, 210, 211

Gastric juice, cause of flow of, 120;
composition of, 125-126; effect on
protein, 126; enzymes in, 128; func-
tions of, 128 ; laboratory problem, how
protein is affected by, 126 ; secretion
of, 127-130

Gastropoda, 523

Gastrula, 286

Generation. See Spontaneous genera-
tion

Genes, change in character of, 339-340 ;
character of, 316; combination in sex
cells, 332-333 ; crossing-over of, 339,
340-341 ; definition of, 306 ; double,
331 ; functions of, 306 ; laboratory
problem to show possible combinations
in cells, 336-337 ; location in chromo-
somes of fruit fly, 312, 332

Geographical evidences, of evolution,
habitats of animals, 385 ; ' Mongolian
Expeditions, 385-387

Geological evidences, of evolution, 381-
384 ; fossils, 379, 381-382

Geotropism, 203

Germ carriers, 397-399, 454-455, 482

Germ plasm, causes of variation, 336-
337, 339-342; continuity of, 336;
effect of environment on, 341-342 ;
theory of, 335-336

Germicide, 402

Germinal variations, transmitted, 312,
339-342

Germination, 279

Gigantism, cause of, 197

Gilbert, W., influence on Harvey, 163

Gills, tadpole, 287

Gland, oil, 173; sweat, 171, 173

Glands, ductless, 191-201 ; endocrine,
191 ; experiment of grafting, 201 ;
meaning of, 118; location in man,
192 ; location in a rat, 193 ; position

558

INDEX

of gastric, 125 ; rate of secretion of,
127; regulation of secretion, 127-128;
relation to digestion, 118, 119. See
Adrenal, Intestinal, Liver, Pancreas,
Parathyroid, Pineal Body, Pituitary,
Reproductive, Salivary

Granular theory, of nature of proto-
plasm, 54

Glottis, 122

Glycogen, in liver, 161

Goiter, and iodine, 194-195; districts,
194-195; endemic, 194; exophthal-
mic, 195

Goldberger, Dr. Joseph, work on vita-
min P-P, 104

Gonads, 200

" Goose flesh," cause of, 172

Gorgas, eradicating yellow fever, 491

Grafting, bud, 258; effect of, 258-259;
in surgery, 259-260 ; process of, 257-
259 ; propagation by, 257-260 ; stem,
257-258 ; tongue, 259

Greeks, contributions to science, 10-12

Growth, of science, 10-17 ; mental, 225

Guard cells, of stomata, 67

Guinea pigs, in breeding experiments,
329

Gymnospermae, classified, 520 ; mean-
ing of, 520

Habit, breaking a, 224-225 ; formation
of, 220-221 ; meaning of, 221

Haemoglobin, 182 ; and oxygen, 146 ;
function of, 88, 146-147 ; in corpuscles,
88

Haemophilia, 148

Hair follicles, origin of, 173

Harvey, William, discoverer of circula-
tion of blood, 163, 164-165 ; influence
of Gilbert on, 163 ; portrait of, 143 ;
theory confirmed by Leeuwenhoek,
19-20

Health, and adaptability, 414-415; and
education, 415-417 ; and longevity,
414 ; disease and, 413-414 ; measure-
ment of, 419 ; science and, 417-419

Health education, need of, 7, 415-417

Heart, auricles of, 152, 154, 159-160;
laboratory study of, 152-153 ; proper-
ties of muscles of, 85, 152, 154 ; struc-
ture of, 152, 154 ; valves of, 152, 154 ;
ventricles of, 152, 154

Hemolysin; antibody, 501

Hepatic vein, 161

Heredity, in Andalusian fowls, 318-320 ;
in four-o'clocks, 320-322 ; in organ-
isms, 333 ; methods of investigating
human, 356-362 ; rise of knowledge of,
318-333 ; versus environment, 369-
370

Herreshoff family, inheritance of, 361

Hexactinellida, 521

Hippocrates,. Father of Medicine, 10-11

Hirudinea, 523

Holothuroidea, 522

Hominidae, 527

Hooke, Robert, first observer of cells,
27 ; microscope of, 27

Hormone, definition of, 133 ; secretin,
133, 191

Horse, evolution of the, 375, 376, 377

Human heredity, difficulty in studying,
357; methods of investigating, 356-
362

Humoral theory, of immunity, 506

Hybrid, appearance of, 319, 324; de-
scendants of, 319-322 ; meaning of,
319, 321 ; proportion in different
generations, 319-322

Hybridization, method of breeding, 351

Hydra, reproduction of, 249-250

Hydrochloric acid, in gastric juice, effect
of, 129-130

Hydrogen, a chemical element, test for,
16

Hydrophobia. See Rabies

Hydrotropism, 204, 205

Hydrozoa, 521

Hygiene, defects revealed by examina-
tion, 416-417; mental, 222-237;
of circulatory system, 167-169 ; of
digestion, 138-141 ; of respiration,
185 ; of skin, 174-175

Hyphae, of mold, 264, 265

Hypocotyl, 278

Immigration, and eugenics, 367-368
Immunity, 504-509; active, 452, 456,
458 ; acquired, 501 ; antitoxins in,
505; Ehrlich's side-chain theory of,
506 ; establishing active, 458-459 ;
establishing passive, 508 ; lysins in,
505 ; meaning of active, 452 ; mean-
ing of passive, 456 ; meaning of per-
manent, 456 ; natural, 506-507 ; of
animals, 345 ; of plants, 347 ; of to-
morrow, 508-509 ; phagocytic theory
of, 504-505 ; racial, 507
Immunization active, 452
Improved Beach plum, development of,

348 T 349, 352, 353
Impulse, nature of nerve, 222-223
Impulses, types of, 215
Incomplete dominance, meaning of, 319
Indigestion, causes of, 138-141, 168
Ingestion, a life function, of amoeba, 43
Infancy, among birds, 298-299; among
insects, 297-298 ; among lower ani-
mals, 295-296; among mammals,
299-300 ; among seed plants, 293-295 ;
in man, 301-303
Infection. See Focal infection

INDEX

559

Inferiority, conflict, nature of, 236 ; pre-
vention of, 236

Influenza, symptoms of, 476 ; trans-
mission of, 476

Infusoria, 521

Inheritance, chromosome theory of, 331-
333; of disease, 368-369; of varia-
tions, 374-375

Inoculation, smallpox, in the Orient, 420-
421 ; introduction into England, 421 ;
method of, 421 ; origin, 421

Insecta, 524

Insectivora, classified, 527

Insects, the young of, 297 ; wasps, 297-
298

Inspiration, definition of, 182

Insulin, in treatment of diabetes, 199

Intelligence quotient, definition of, 228-
229

Intelligence, definition of, 227 ; measure-
ment of, 228-229; of students of
Oxford University, 357 ; relation of
progress in school to, 229-230, rela-
tion of vocations to, 230-231

Intercellular materials, 74

Intestine. See Large intestine, Small
intestine

Intestinal gland, in relation to digestion,
118

Intestinal juice, 131, 132

Introspection, advantages of, 236 ; dis-
advantages of, 236

I. Q. 228—229

Irritability, cause of, 202-203; in
amoeba, 44HL6 ; in animals, 202-203 ;
in green cell, 41 ; in Paramecium, 50-
51 ; in plants, 202 ; in man, 205

Islands of Langerhans, 198 ; location of,
199 ; value of, 199

Isogametes, defined, 267, 268

Jenner, Edward, discovery of vaccina-
tion by, 421-422
Juke family, history of, 358-359

Kallikak family, history of 359-360
Kanred wheat, how produced, 347 ;

increased yield of, 351
Katabolism, in cell, activities, 60 ; mean-
ing of, 59
Kidneys, elimination of waste through,

170; excretory function of, 175-176;

position, 175 ; secretion of urine by,

170, 175 ; structure of, 175
Kitasabo, cultivation of tetanus bacilli

by, 460
Klebs, discovery of diphtheria bacilli by,

450
Koch, discovered cause of tuberculosis,

438-440 ; effect of his discovery, 440 ;

experiments with guinea pigs, 439-

440 ; portrait of, 437 ; postulates of,
440; tuberculin test prepared by,
446-447

Labor, physiological division of, 66-67

Lacteals, 136-137, 166

Lamarck, Jean de, theory of evolution,
371-373

Lamarckian theory, of evolution, 371-373

Langerhans, islands of. See Islands of
Langerhans

Large intestine, 135 ; absorption from,
138 ; bacteria of, 135, 140 ; bacterial
action in, 135 ; function of, 133, 134 ;
divisions of , 119, 135; relation to con-
stipation, 135, 139

Larynx, 178, 179

Laveran, discoverer of malarial parasites,
481

Laws, of inheritance (Mendel's), 322-330

Lawton blackberry, berries produced
from, 348, 349

Laxatives, kinds, 139-140 ; use, 139

Layering, method of vegetative propaga-
tion, 260

Lazear, work on yellow fever, 487-491

Leaf, functions of, 70

Learning, laws of, 223-224

Leeuwenhoek, contribution to contro-
versy on origin of life, 240-241 ; im-
proved microscope, 19-20

Lemuroidea, 527

Levels of reactions, 216, 217 ; diagrams
to show, 218, 219, 220

Life, origin of, 239-245 ; ancient idea,
239 ; a present-day theory of, 245

Ligaments, functions, 80-81

Lindbergh, contribution to science, 1

Linnaean system, of classification, 510-
511

Linnaeus, Carolus, system of classifica-
tion by, 510-511

Linin, in nucleus, 57

Lipase, an enzyme, 38 ; steapsin, 131

Lister, Sir Joseph, contribution to sur-
gery, 4

Little Club wheat, improvement of, 350

Liver, circulation through, 160-161 ;
function of, 132, 161 ; relation to diges-
tion, 118; secretion of, 132; storage
of sugar in, 161

Locomotion, of amoeba, 46 ; of Parame-
cium, 49

Lockjaw. See Tetanus

Loeb, J., on artificial parthenogenesis,
271-272

Loeffler, isolation of diphtheria bacilli
by, 450

Lungs, flow of blood through, 160; in-
fection of. See Pneumonia and Tuber-
culosis ; laboratory problem on struc-

560

INDEX

ture and function of, 180-181 ; move-
ment of, 182 ; protection of, 179 ; red
corpuscles, 179 ; size, 182 ; structure
of, 179 ; volume of air in, 183

Lymph, circulation of, 165-166 ; fluid,
137 ; pressure of, 166 ; source of, 165 ;
spaces, 166 ; vessels, 165-166

Lymph gland, function of, 167

Lymph nodes, bacteria in, 167; func-
tions of, 167; position of, 166-167;
structure of, 167

Lymphatic system, 163-169

Lymphatics, 137 ; functions of, 166-167 ;,
valves in, 166

Lysins, use of, 501 ; kinds of, 501

M. A., 228

Macronucleus, in Paramecium, 49-50

Malaria, 480-486 ; cause, 482 ; diagnosis

of, 485 ; history of, 481-182 ; investi-
gation of cause, 15 ; method of spread,

482 ; nature of, 484-485 ; prevalence

of, 480-481 ; prevention of, 486 ;

treatment of, 485
Malarial parasite, life cycle of, 482H:84 ;

multiplication of, 483-484
Malnutrition, cause of, 104 ; effect on

embryo, 313
Malpighi, drawing of circulation by, 151 ;

movement of blood in capillaries first

seen by, 164
Malpighian layer, of skin, 172
Malthus, effect of essay on Darwin, 373 ;

Essay on Population, 343
Mammalia, classified, 526-527
Mammals, development of embryo, 299-

300 ; food of, 300 ; infancy, 299-301 ;

years, of dependence, 300-301, 302
Man, infancy in, 301-303 ; protection of

young, 30
Manufacture, of food, by green plants,

36-38
Marconi, Guglielmo, portrait of, 1
Marsupialia, animals of Order, 526
Mastication, importance of, 123 ; process

of, 120
Mastigophora, 521
Mastodon, restoration of, 379
Maturation, of egg, 264; of sex cells of

fruit fly, 269 ; of sperm, 264 ; process

of, 268-270 ; variation due to, 285
McCollum, investigation on diets, 93-

95
Measles, after-effects, 478 ; method of

spread, 478 ; prevention of, 478
Measurement, of health, 419
Media, definition of bacterial, 395 ; for

cultivation of bacteria, 396-397
Medicine, early practices of, 3, 10-13
Medulla, oblongata, description of, 207 ;

function of, 207

Membrane, meaning of, 75 ; mucous, 75 ;
serous, 76

Mendel Gregor, experiments with peas,
322-326, 327-329; portrait of, 318;
rediscovery of writings, 330

Mendelian laws, of dominance, 322-324 ;
of segregation, 324-326 ; of unit
characters, 327-330 ; of heredity, sum-
marized, 331

Mental age, 228

Mental hygiene, 227-237

Mental poise, cause of lack of, 233-235 ;
need of, 227, 233 ; relation to disease,
502-503

Mesentery, function of, 77

Mesoderm, of embryo, 286 ; development
of, 286 ; systems formed from, 286

Metabolism, basal, 193; in cell, 59-60;
kinds, 187 ; meaning of, 59-60 ; of
carbohydrates, 188 ; of fats, 190 ; of
proteins, 188-190

Metamorphosis, of frog, 287

Metaphase, stage in cell division, 62

Metchnikoff, on bacteria of putrefaction,
140 ; theory of immunity, 504-505

Method, modern scientific, 13-15

Micron, unit of measurement, micro-
scopic work, 392-393

Micronucleus, in Paramecium, 47-50, 248

Micropyle, of egg, 270, 276

Microscope, 19-25 ; care of, 23-24 ;
compound, 20 ; history of develop-
ment, 19-20 ; Hooke's, 27 ; labora-
tory problem on use of, 24-26 ; parts
of, 21-23 ; rules for focusing, 24

Milk, acidopholus, 140 ; increase in
products of, 344 ; influence on ty-
phoid, 467 ; laboratory problem to
determine bacterial content, 401

Minerals, foods containing, 96 ; insuffi-
ciency, 95 ; need of, 95

Mitosis, in animal cell, 61-63 ; in plant
cell, 63, 64 ; laboratory study of, 63 ;
process of, 60-63

Mitral valve, of heart, 160

Mold, laboratory problem, on spore
formation, 251-252 ; hyphae, 251 ;
mycelium, 257 ; rhizoid, 251 ; sexual
reproduction in, 264, 265 ; sporangium
of, 251-252, 253

Molecular theory, 35

Molecules, laboratory problem to show
movement of, 35

Mollusca, classified, 523 ; meaning of,
523

Mollusks, the young of, 296

Mongolian expeditions, 385-387

Monotremata, 526 ; duckbill, 513

Morgan, T. H., on heredity, 55; por-
trait of, 318; work on heredity, 14;
work on mutations in fruit flies, 312

INDEX

561

Morphological evidences, of evolution, in
structure of animals, 387-388

Morphology, meaning of, 17

Morula, 285

" Mother of vinegar," 391

Mouth, of man, 120-121 ; structure of,
120; use of, in digestion, 120-121

Mucous, lining of nasal passages, func-
tion of, 178

Muscle tissue, 85-86; cardiac, 85;
cross-striated, 85 ; function of, 85-86 ;
structure of, 83-85 ; unstriated, 85

Muscle, laboratory problems on struc-
ture of skeletal, 83-84; laboratory
problem on structure of smooth or in-
voluntary, 84

Muscles, antagonistic, 86 -

Muscular action, antagonistic, 85-86

Mutants, causes of, 377 ; examples of
occurrence, 337-339 ; importance in
breeding, 353-354 ; meaning of, 337

Mutation theory, of evolution, 376 ; and
natural selection, 377

Mycelium, in mold, 251

Myriapoda, 524

Myxedema, 194

Narcissus, laboratory study of epider-
mis of leaf of, 30-31

Nasal passages, removal of dust by, 178 ;
warming and moistening air by, 178

Natural immunity, meaning of, 506 ; of
races and individuals, 507

Natural selection, 373-375 ; and muta-
tion theory, 377 ; Darwin's theory of,
373-376; objections to theory of, 376

Navel orange, development of, 349

Needham, experiments to prove spon-
taneous generation, 241

Negri bodies, in rabies, 433, 435

Nemathelminthes, 522

Nerve centers, 208

Nerve tissue, in man, 86 ; unit of struc-
ture, 86-87 ; work of, 86

Nerves, function of, 208-209 ; motor, 210 ;
pathway of, 209-211 ; sensory, 209

Nervous reactions, importance of, 223 ;
kinds of, 215, 216-221; laboratory
study of, 225 ; nature of, 216-217

Nervous system, 202-214; autonomic
portion of, 210-211 ; cellular structure
of, 208-210; cerebro-spinal or central
portion of, 205-210 ; effect of tobacco,
236-237; effect of alcohol, 237; main
subdivision of, 205 ; principle of
operation of, 205 ; structure of, 208-
210 ; studies of, man and other verte-
brates, 211-212 ; the methods of study-
ing, 212-213

Neuron, associative, 209 ; description of,
208 ; diagram of, 209

Nicolaier, discovery of tetanus bacillus,

460
Nitrification, process of, in soil, 406-407
Nitrogen, cycle, 406, 410 ; fixed by

bacteria, 406, 407-409
Nitrogen, fixation, 407-409
Nodes. See Lymph nodes
Nodules, use of root, to soil, 408
Noguchi, Hidego, 2-3 ; work on yellow

fever, 491,492
Nostrils, 178
Nuclei, polar, 276, 277, 278; sperm,

275
Nucleoplasm, structures found in, 57
Nucleus, of cell, 27-28 ; endosperm, 278 ;

egg, 277 ; generative, 275 ; tube, 275 ;

work of, 57-58
Nutrients, food, 91-104; definition of,

91-92; table of, 94
Nutrition, of Paramecium, 48-49
Nutritive processes in organisms, pur-
pose of, 34

Objections, to vaccination, 423, 427

Offspring, cause of differences among,
315 ; character of, 306-317

Oil glands, 173

Onion cells, laboratory study of, 25-26

Ontogeny, history of individual, 388-
389

Onychophora, 523

Oogenesis, meaning of, 270

Ophiuroidea, 522

Opsonins, effect on bacteria, 500, 502 ;
test for amount of, 502

Orange, navel, 349

Organ, definition of, 73

Organic evolution, 371-389 ; Darwinian
theory . of, 373-376 ; embryological
evidences of, 388-389; de Vries'
theory of, 376-377; factors in, 371;
geographical evidences, 385-386 ; ge-
ological evidences, 381-384; history
of, 371 ; Lamarckian theory of, 371-
373 ; morphological evidences of, 386-
387 ; vestigial evidences of, 387-388

Organism, offspring of simple, 292-293

Organisms, heredity in, 333 ; purpose of
life processes in, 34

Organs/ of digestion, 118-119; 125-135

Origin of Species, by Darwin, 373

Osmosis, in absorption of food, 136, 137 ;
in root hair, 69 ; in photosynthesis,
meaning of, 34 ; process of, 34-35

Osterhout, on heredity, 55

Ova, of frog, 283

Overproduction, of species, 373

Ovules, in flower, 274, 276-277, 279

Oxygen, a chemical element, test for,
16 ; importance to life, 241-242

Oxyhaemoglobin, 147

562

INDEX

Palate of man, 120

Paleontology, 378

Palisade cells, of leaf, 67

Pancreas, digestive secretions of, 131 ;
internal secretion of, 199 ; relation to
digestion, 118. See Diabetes, Insulin

Pancreatic juice, enzymes of, 131

Papillae, of tongue, 120; functions of,
173

Parasite, definition of, 252 ; group of
bacteria, 393-394

Paramecium, conjugation of, 49-50, 248,
267-268; effect of alcohol on, 50;
irritability ofp 50-51 ; laboratory
study of, 46-47 ; locomotion of, 49 ;
mode of defense, 50-51 ; nutrition of
48-49 ; reproduction of, 49-50

Parathyroid glands, location of, 196 ;
relation to metabolism, 196; secre-
tion of, 196. See Tetany

Parental care, shown by, birds, 298-299 ;
fishes and frogs, 296 ; insects, 297-298 ;
mammals, 299-301 ; man, 301-304

Parenthood, development of, 303-304

Park, Dr. W. H., inoculations with toxin-
antitoxin, 452-453

Parotid gland, in mouth, 121

Parthenogenesis, 271-272

Passive immunity, acquiring, 508

Pasteur, Louis, 3 ; ideals of, 435-436 ;
treatment for rabies, 430-432 ; work
to disprove spontaneous generation,
242-244

Pavlov, experiments on digestion, 138-139

Payne, " Habits and Practices in Acci-
dent Prevention and Health," 419,
the appendix

Peas, sweet, Mendel's experiments on
heredity of, 322-326 ; 327-330

Pelecypoda, 523

Pellagra, deficiency disease, 104

Pepsin, 128

Pepsinogen, 128

Peptic gland, relation to digestion, 118

Peptone, form of protein, 128

Pericardium, of man, 76

Periosteum, of bone, 78

Peristalis, described, 123

Peritoneum, of man, 76

Perspiration, 170

Petri, R. J., devised Petri dish, 396

Phagocytes, function of, 146-147, 500;
504-505

Phagocytic theory, of immunity, 504-505

Phagocytosis, 147

Pharynx, 122

Photosynthesis, meaning of, 37 ; process
of, 36, 37

Phototropism, laboratory problem to
show, 203 ; shown by amoeba, 46

Phrenology, 5, 214

Phylogeny, history of entire race or
group, 388-389

Phylum, in taxonomy, 516

Physics, and its relation to biology, 15-16

Physiological functions, of organism, 34

Physiology, meaning of, 17

Pigment, in skin, 172

Pineal body, effect of injury to, 200;
location of, 200

Pisces, animals of class, 525

Pituitary gland, location of, 196; rela-
tion to growth, 196-197. See Acro-
megaly, Dwarfism, Gigantism

Placenta, animals, 289, 291 ; of plants,
274, 278

Plant, and animal breeding, 343-353 ;
experiments by Mendel, 322 ; organs of
flowering, 273

Plants, cellular nature of , 30-31 ; growth
of seed, 293-295 ; manufacture of
food, 36-38 ; reproduction of higher,
273-279 ; specialization in higher, 69-
72 ; storage of food in, 70-71

Plasma, composition of blood, 145

Plasma membrane, function of, 58 ; of
cell, 32

Plasmodium malariae. See Malarial
parasite

Platelets.' See Blood platelets

Platyhelminthes, 522

Pleurae, of man, 76

Pleurococcus, diagram of, 33 ; laboratory
problem on, 31 ; reproduction of, 247

Plexus, 210

Plum, development of new species of,
348-349

Plumcot, how produced, 349

Plumule, 278

Points, breeding for, 349-350

Poise, mental. See Mental poise

Polar, nuclei, 276, 277, 278 ; bodies, 270

Pollen, agencies to scatter, 276 ; effect of,
277-278; grains, 275, 276, 277;
laboratory study of effect of sugar solu-
tion on, 275 ; nuclear division in, 276 ;
production of, 275 ; tube, 275, 276, 277

Pollination, agents 'of, 293 ; artificial
method of, 352 ; process of, 276

Polyneuritis, cause of, 100 ; cure for, 100

Population, Malthus' Essay on, 343

Pore, of skin, 173

Porifera, classified, 521 ; meaning of, 521

Portal, circulation, 160-161 ; vein, 161

Postulates, of Koch, 440

Potatoes, propagation of, 350

Pouchet, on spontaneous generation,
242-244

Precipitins, function of, 501-502

Preservation of food, discussed, 399

Primates, classified, 527 ; animals of
order of, 527

INDEX

563

Primroses. See Evening Primrose

Priority, law of, 514-515

Production, breeding for increased, 351 ;
of new species, 347-349

Progress, in school, relation of intelli-
gence to, 229-230

Propagation, methods of animal, 353-
354; methods of plant, 352-353; of
dahlia, 349-350 ; of potato, 350 ; vege-
tative. See Vegetative propagation

Prophase, stage in cell division, 62

Protease, an enzyme, 38 ; erepsin, 132 ;
trypsinogen, 131

Protection, of young, 292-304

Protein, foods containing, 95 ; formation
of, 38 ; insufficiency of, 93, 95 ; labora-
tory problem on effect of gastric juice
on, 126; laboratory problem on rela-
tion of time of digestion to size of,
126 ; laboratory problem on rate of
digestion of different animal, 127 ;
manufacture of, 37-38 ; metabolism of,
188-190 ; process of synthesis, 37-38 ;
product of protein-synthesis, 37-38

Proteose, form of protein, 128

Protoplasm, cause of variety in, 306-^-
307; cause of likeness in, 307-308;
characteristics of, 29-30, 55-57 ; dis-
covery of, 28 ; functions of different
parts of, 57-60; effect of alcohol on,
50; named, 28; specialization of, 5. 1 -
52 ; structure of, 53-55 ; reticular
theory of, 53-54 ; alveolar or foam
theory of, 54 ; granular theory of, 54 ;
variety in, 306-308

Protozoa, classified, 520-521

Pteridophyta, classified, 519-520

Pterodactyl, prehistoric flying reptile,
382-383

Ptomaines, 495

Ptyalin, enzyme of saliva, 121

Pulmonary, artery, 153 ; circulation,
160

Pulse, cause of, 156 ; laboratory study
on rate of, 156-157

Punnett squares, 328, 330, 332

Purkinje, discoverer of protoplasm, 28

Pustules, of smallpox, 423, 425

Pyloric valve, of stomach, 125

Pyorrhea, cause of, 110-111

Pyrenoids, structures in Spirogyra, 32

Quality, breeding to improve, 330

Rabies, cure of, 434 ; discovery of treat-
ment by Pasteur, 430-432 ; effect on
animals, 433 ; eradication of, 434 ;
nature of, 432-433 ; preparation of
vaccine for, 43 J ; prophylatic or pre-
ventive treatment of, 434-435 ; trans-
mission of, 433

Race improvement, necessity of, 362-
363 ; suggestions for, 363-368

Reactions, conscious, 219 ; glandular,
221-^222 ; in learning, 219 ; levels of,
216-217, 218, 219, 220; types of, 216-
217. See Nervous reactions

Recapitulation, doctrine of, 388-389

Recessive character, defined, 324 ; list
of, 333

Red corpuscles, in lungs, 179

Redi, Francesco, experiments on spon-
taneous generation, 239-240

Reduction division. See Maturation

Reed, Major W., work on yellow fever,
487-491

Reflex, conditioned, 217-219 ; develop-
ment by conditioned response, 218 ;
nature of, 217-219 ; simple, 215

Refrigeration of foods, 399

Regeneration, in amoeba, 56 ; in higher
animals, 257 ; in lower animals, 256,
257 ; similarity to vegetative propaga-
tion, 255-256; in Stentor, 56; in
Stylonychia, 56 ; in Uronychia, 56

Rennin, 128, 129

Reproduction, asexual. See Asexual re-
production

Reproduction, by binary fission, 247-
248 ; by budding, 248-250 ; by spore
formation, 250-251 ; by vegetative
propagation, 255-263 ; by two special
cells, 264 ; necessity in cells, 246-247 ;
of amoeba, 44, 248 ; of animals, 281-
291 ; of bacteria, 247 ; of birds, 288 ;
of frog, 282-287; of higher plants,
273-279; of mammals, 288-291;
of mold, 264, 265 ; of Paramecium,
49-50; 248; 267-268; of Pleuroccus,
247 ; of Spirogyra, 247-248, 265-267

Reproduction, sexual. See Sexual Re-
production

Reproductive glands, relation to normal
development, 200-201 ; secretion of,
200

Reproductive processes, in organisms,
purpose of, 34

Reptile, flying, 382

Reptilia, animals of order, 526

Respiration, 177-185 ; definition of, 182 ;
external, 183 ; hygiene of, 185 ; in-
ternal, 183 ; in plants, 36, 38-39 ; of
amoeba, 44; of iish, 177-178; of
insects, 177 ; of higher animals, 178 ;
products of, 182-183, 184 ; rate of, 183

Respiratory, movements, 181-182 ; pas-
sages, irritation of, 179-180

Respiratory tract, diseases of, adenoids,
179 ; tonsillitis, 180

Response, laboratory problems, of plants
to gravity, 202-204 ; to sunlight, 203 ;
to water, 204

564

INDEX

Reticular theory, of nature of protoplasm,
54

Rhinoceros, prehistoric, 378

Rhizoda, classified, 521

Rhizoid, of mold, 251

Rhizomes, plants with, 261 ; propaga-
tion by, 261

Rhythmic segmentation, of small intes-
tine, 130

Rickets, cause, 102-103 ; prevention and
cure of, 100, 103

Rodentia, classified, 527

Rootstock, plants with, 261 ; propaga-
tion by, 261

Root hairs, of plants, 69

Ross, Major R., investigation of malaria,
481-482

Rotation of crops, need for, 409-411

Round worms. See Nematheliminthes

Roux, isolation of diphtheria toxin, 451

Runners, use of, in propagating, 260-261

■ Saliva, composition of, 121-122; diges-
tive action of, 121-122 ; enzymes of,
121 ; factors influencing secretion of,
121 ; functions of, 120-121 ; secretions
of, 121

Salivary glands, position of, 120; func-
tion of, 120-121

Saponification, in the digestive process,
131

Saprophytes, group of bacteria, 251, 394,
499

Scarlet fever, probable cause of, 458 ;
test to determine susceptibility to, 458 ;
transmission of, 459

Schleiden, knowledge of cells, 28

Schultze, contribution to cell theory, 29

Schwann, Theodore, work on cells, 28

Science, age of, 1-3 ; aim of, 6 ; and
health, 417-419 ; contributions by
Greeks, 10-12; growth of, 10-11; of
primitive man, 10

Scientific method, modern, 13-15 *

Scurvy, 97; cause of, 100, 102; treat-
ment for, 100, 102

Scyphozoa, 522

Secretagogues, 128

Secretin, 133

Secretions, internal, 191-192 ; of green
cell, 40

Seed, appendages, 294 ; differ from eggs,
281; dispersal of, 294-295; food re-
serve of, 294-295 ; formation of, 278-
279 ; protection of, 294

Segmentation, rhythmic, of small intes-
tine, 130

Segregation, of genes during maturation,
325, 328 ; Mendel ian law of,, 324-326

Selection, artificial, importance in plants,
352

Self-acting nervous system. See Au-
tonomic nervous system

Self-pity, as trait of personality, effect of,
236

Serum of blood. See Blood

Sexual characters, secondary, 281-282

Sexual reproduction, in higher plants and
animals, 264, 268, 273-291 ; in mold,
264-265 ; meaning of, 264 ; in Parame-
cium, 267-268 ; in Spirogyra, 265-267

Shick test, application of, 457 ; of sus-
ceptibility to diphtheria, 453

Side-chain theory, of immunity, 506

Sieve tubes, of plants function of, 68

Simiidae, 527

Simon, Theodore, tests by, 228

Sirenia, animals "of Order, 527

Skin, functions of, 173-174 ; hygiene of,
174-175 ; laboratory study of the, 170-
171 ; organ of elimination, 170, 173-
174 ; sense organ, 173 ; structure of,
172-173 ; thickness of, 172

Slant, agar, 397

Slips, method of vegetative propagation,
255-256

Small intestine, absorption from, 136-
137 ; adaptations of, 136-138 ; diges-
tion in, 130-131,132-133, 135; diges-
tive juices of, 132-133 ; folds in, 136 ;
glands of, 131; movements of, 130;
villi of, 136, 137

Smallpox, cases and deaths in United
States, 424 ; epidemics of, 420 ; history
of, 420 ; history of inoculations against,
420-421 ; nature and symptoms of,
423, 425 ; preparation of vaccine for,
426 ; prevention, 425-426 ; spread,
425 ; value of vaccination, 426-427.
See Vaccination

Soil, bacteria of, 405-411 ; conservation
of, 411

Somatic cells, 269

Somatic variations, not transmitted, 310

Spallanzani, on spontaneous generation,
241

Spawning, of fish, 283-284; of frogs,
282-283

Species, production of new, 347-349 ; in
taxonomy, 517

Species and Varieties, by De Vries, 376-377

Species, Origin of, by Darwin, 373

Specialization, in higher plants, 69-72

Sperm cell, characteristics of, 268

Spermatogenesis, meaning of, 269

Spermatophyta, 520

Sperms, production of frog, 285

Sphincters, 125

Spillman, production of hardy wheat by,
350

Spinal cord, description of, 207-208;
diagram of cross section, 208 ; func-

INDEX

565

tion of, 208 ; level of reactions of, 218,
219, 220; relation to reflexes, 208;
structure of, 207-208

Spireme, formation of, in cell division,
61-62

Spirilla, form of bacteria, 392

Spirochaete, causative organism of yel-
low fever, 492

Spirogyra, description of, 31 ; labora-
tory problem on the cells of, 31-33;
meaning of, 32 ; reproduction of, 247-
248 ; 265-267 ; specialized structures
of, 32 ; typical green cell, 31-37

Spleen, activity of, 200 ; location of, 200

Split-proteins, poisonous, formation of,
495

Sponges, use of bacteria in preparation
of, 404

Spontaneous generation, controversy on,
242-244 ; experimental evidence on,
239-241 ; 242-243 ; theory of, 239

Sporangia, laboratory problem, in vari-
ous molds, 252

Spore, of bacteria, denned, 395

Spore-formation, cause of, 250 ; of yeast
cells, 250 ; reproduction by, 250

Sport. See Mutants

Sporozoa, 521

Stanford Revision of Binet-Simon scale,
228

Starch, digestion of, 130

Steapsin, 131

Stentor, regeneration of, 56

Stomach, function of, 129 ; glands of,
125-126; of frog, 115; parts of, 152;
shape of, 129 ; valves of, 125

Stomata, of leaf, 67, 69 ; guard cells of,
67 ; position of, 67

Storage, of food in plants, 70-71

Structure, of amoeba, 42 ; of Paramecium,
46-47 ; of cell, 53-55 ; of protoplasm,
55-57 ; of higher plants, 66-72

Struggle for existence, 373

Stimulation, of glands, chemical, 121,
128; mechanical, 121; psychical, 121,
127

Stimulus, meaning of, 40 ; of glands.
See Stimulation

Stylonychia, regeneration of, 56

Sublingual gland, in mouth, 121

Submaxillary glands, in mouth, 121

Succus entericus, 131, 132

Sunlight, in relation to rickets, 103

Supporting tissues, in man, 77; in
plants,, 71 ; laboratory problem on,
80

Surgery, antiseptic, 4; aseptic, 45;
early, 3, 11-13; grafting in. 259-260
modern methods in, 13-15
Survival of the fittest, 374

Sweat glands, 171, 173

Sweet peas, Mendel's experiments in

heredity of, 322-326 ; 327-330
Symbiosis, denned, 394
Sympathetic nervous system. See.An-

tonomic nervous system
Synapse, properties of, 208, 209, 210
System, circulatory, 151-162 ; diagram
of circulation, 155 ; nervous system,
202-214 ; lymphatic, 163-169 .
System development in embryo, 286
Systema Naturae (Linnaeus), 511
Systemic circulation, of blood, 159-160

Table, of caloric needs, 105 ; of foods
containing minerals, 96 ; of food
nutrients, 94 ; of vitamins, 101

Tartar, on teeth, 109

Taste-buds, importance of, 120

Taxonomy, meaning of, 512 ; difficulties,
513-514

Teeth, arrangement of, 108-109 ; causes
of decay, 109-112; causes of mal-
formation, 180; dental care, -110-.
Ill; kinds of, 107-108; individual
care of, 109-111; laboratory problem
on condition of teeth, 112 ; number of,
107-i08 ; of adults, 108 ; of children,
108, 109 ; relation of diet to, 111-112 ;
structure of, 107, 108 ; tartar on, 109

Telophase, stage in cell division, 63

Temper, bad effect of, 236 ; reason for,
235-236

Terman, revision of Binet-Simon scale
by, 228

Tendons, use of, 81

Tetanus, antitoxin, 461 ; bacilli, 460 ;
cause of, 459-460 ; discovery of bacil-
lus of, 460 ; entrance into body, 460 ;
nature of, 461; occurrence, 460;
prevalence, 459 ; prevention, 462 ;
treatment, 461

Tetany, cause of, 196

Thallophyta, classified, 518-519 ; mean-
ing of, 33 ; plants of, 33

Thermotropism, shown by amoeba, 46

Thigmotropism, shown by amoeba, 46

Thoracic duct, 165

Thymus gland, location of, 199 ; relation
to growth, 199

Thyroid gland, disturbances of secretion,
194-195; grafting of, 193-194; in-
fluence on growth, 194; position of,
192-193 ; secretion of, 193. See also
Cretinism, Cretins, Goiter, Myxodema

Thyroxin, secretion of thyroid, 194

Tidal air, 183

Tissue, blood, 87, 145-148 ; contractile,
83 ; use of epithelial, 75-77 ; functions
of, 88-89; muscular, 85; nerve, 86-
87 ; of leaf, 68-69

Tissue fluid, 165

566

INDEX

Titanotheres, prehistoric mammal, res-
toration of, 379

Tobacco, effect on nervous system, 236-
237, 169 ; use of bacteria in curing, 405

Tongue, a sense organ, 120

Tonsillitis. See Tonsils

Tonsils, enlargement of, 180 ; infection
of, 180 ; colds result from, 475-476

Tourniquet, when to use, 168

Tower, experiment of effect of environ-
ment of germ plasm, 341-342

Toxin-antitoxin, discovery of value of,
452-453 ; isolation of diphtheria, 471 ;
" of tuberculosis, 442

Trachea, 179, 178

Tracheids, in a leaf, 68, 70

Traits, ancestral, effect of environment
on, 313-315

Transfusion, of blood, 149

Trichocysts, of Paramecium, function of,
47, 50-51

Tripe, meaning of, 126

Tropism, in amoeba, 45^46 ; meaning of,
45 ; kinds of, 45-46, laboratory prob-
lems to show plant, 203-204 ; use of,
204

Trudeau, 440-^442 ; investigations of
tuberculosis, 441-442 ; method of
treatment for tuberculosis, 442 ; por-
trait of, 437 ; sanitarium of, 441, 442

Trypsinogen, 131

Tubercle bacilli, discovery of, 438-439 ;
effect of, 442, 443; staining of, 438;
when found, 439

Tuberculin test, devised by Koch, 446-
447 ; for cows, 444, 445

Tuberculosis, acquired from milk, 445 ;
bacilli of, 438, 439 ; causative organ-
ism of, 442 ; conditions favoring de-
velopment, 443-444 ; diagnosis, 444 ;
discovery of cause of, 438-440; eco-
nomic importance of, 448 ; eradica-
tion of, 444 ; experiments on spread
of, 437-438; immunity to, 442-443;
in relation to heredity, 443, 448 ;
mortality in England and Wales, 445 ;
mortality in United States, 443 ; of
animals, 444 ; prevalence, 448 ; pre-
vention, 446-448 ; spread of, 444-445 ;
symptoms of, 444 ; treatment of, 446 ;
types of, 442; vaccination for pre-
vention of, 447-448

Tubers, propagation by, 261-262

Tubules, of kidneys, 175

Tulip, laboratory study of parts of,
273-274

Twins, causes of identical, 314, 370

Tyndall, John, apparatus and experi-
ment to disprove spontaneous genera-
- tion, 244-245 ; importance of experi-
ment, 245

Typhoid, 464-472 ; bacilli, 464 ; carriers
of, 465 ; cause of, 464 ; diagnosis of,
466-467; epidemic, 469-472; food
infection, 467 ; immunity to, 469 ;
" Mary," 465 ; milk infection, 467,
nature of, 464-465 ; prevalence, 464 ;
prevention of, 468 ; protection of
body against, 465 ; routes of infection,
467-468 ; symptoms of, 464 ; trans-
mission of, 467-468 ; vaccination and,
469

Ultra-violet rays. See sunlight
Ungulata, classified, 527 ; animals of

order, 527
Unit characters, 318, 327-330
Urea, 170, 172-173; formation of, 161
Ureters, position of, 175 ; function of, 175
Urine, 170

Uronychia, regeneration of, 56
Uvula, 120

Vaccination, small pox, decrease of small-
pox in Prussia and Austria due to, 422 ;
history of, 421-422 ; introduction into
America, 423 ; objections to, 423, 427 ;
results of compulsory, 425-426 ; ty-
phoid, 469 ; value of, 426-427, 508

Vaccine, for rabies, 432 ; for smallpox,
426 ; preparation of, 426, 508

Vacuole, function of contractile, 59 ;
function of food, 59 ; structure of food,
58-59

Valve, mitral, 160 ; in veins, 158

Variations, germinal, 312, 339-342; in
species, 374 ; inheritance of, 374-375 ;
somatic, 308-310

Varicose veins, cause of, 168

Varieties, species and, of de Vries, 376-
377

Vascular, and supporting tissues of leaf,
laboratory problem, 68-69

Vegetative propagation, Artificial meth-
ods of, by cuttings, 255-256 ; by graft-
ing, 257, 260; by regeneration, 256-
257 ; Natural methods of, by bulbs,
262-263; by layering, 260; by rhi-
somes, 261 ; by runners, 260-261 ; by
tubers, 261-262

Veins, direction of blood flow in, 157-
160; hepatic, 161; portal, 161;
pressure in, 158-159 ; valves in, 158 ;
varicose, 168

Vena cava, lower or inferior, 153, 160;
upper or superior, 153, 160

Venous blood, 144

Ventilation, methods of, 185

Ventricles. See Heart

Vermiform appendix, 134-135

Vesalius, contributions to surgery, 12,
13 ; knowledge of circulation, 164

INDEX

567

Vessels, blood, laboratory study of, 151

Vestigial evidence, of evolution, traces or
rudiments of organs in higher animals,
387

Villemin, J. A., experimental research in
tuberculosis, 437-438

Villi, described, 136, 137

Vinci, Leonardo da, scientific work of,
163-164

Virus, filterable, 393 ; of smallpox, 423-
424

Vitamins, diseases caused by deficiency
of, 97-99 ; names of, 96-99, 101 ;
list of foods containing, 101 ; present-
day knowledge of, 99-100, 102-104;
sources of, 101

Vocations, relation of intelligence to, 230-
231

Voice-box, 178

Von Behring, discovery of diphtheria
antitoxin, 451-452

Von Haeckel, on recapitulation, 388^-389

Von Leeuwenhoek, improved micro-
scope, 19-20 ; contribution to contro-
versy on origin of species, 240-241

Von Mohl, Hugo, description of cell by,
28

Vries; Hugo de. See de Vries

Wasp, care of their young, 297-298
Water, need of drinking, 167-168
Waugh, C. W., intelligence test to motor-
men, 231

Weismann, portrait of, 335 ; theory of

germ plasm, 335-336
Wheat, Little Club, 350
Whooping cough, after-effects, 478;

method of spread, 478
Widal test, in typhoid fever, 467
Wilson, E. B., on heredity, 55
Windpipe, 122
Woodruff, L. L., experiments with Para-

mecia, 50
Woods, study of royal families by, 357-

358
Woody fibers, of plants, use of, 71
Worry, causes of, 234-235 ; effect of,

233-234
Wounds, disease through, 497

Xerophthalmia, cause of, 99 ; treatment

for, 98, 99
Xylem, conductors of water, 69

Yeast cells, formation of spores in, 250 ;

laboratory study of budding in, 248-

249
Yellow fever, 486-492; c.ause of, 492;
- commission, 487 ; history of control,

487-491; history of, 486-487; later

investigations, 492 ; prevalence of,

486-487
Young, protection of, 292-304

Zygopore, defined, 264-265 ; 266
Zygote, defined, 264, 268

'/- 3 - V - -£

/ ^7

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Texts

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "Advanced biology"

See other formats